tests: 'system_emulated' nox session fails in clean environment

[tseaver]

/cc @crwilcox

$ git remote -v
origin	git@github.com:googleapis/python-api-core (fetch)
origin	git@github.com:googleapis/python-api-core (push)
$ git log -1
commit 3b0912a08f115f352bac65167912400e55ef857e (HEAD -> main, origin/main)
...
$ env | grep GOOGLE || echo Not Set
Not Set
$ env | grep GCLOUD || echo Not Set
Not Set
$ env | grep PROJECT || echo Not Set
Not Set
$ nox -s system_emulated -- -x
nox > Running session system_emulated
nox > Creating virtual environment (virtualenv) using python3.8 in .nox/system_emulated
Google Cloud SDK 358.0.0
beta 2021.09.17
bigtable 
bq 2.0.71
cloud-datastore-emulator 2.1.0
cloud-firestore-emulator 1.13.0
cloud-spanner-emulator 1.2.0
core 2021.09.17
gsutil 4.68

All components are up to date.
nox > python -m pip install --pre grpcio
Executing: /home/tseaver/projects/agendaless/Google/google-cloud-sdk/platform/bigtable-emulator/cbtemulator --host=localhost --port=8789
[bigtable] Cloud Bigtable emulator running on 127.0.0.1:8789
nox > python -m pip install mock pytest google-cloud-testutils -c /home/tseaver/projects/agendaless/Google/src/python-bigtable/testing/constraints-3.8.txt
nox > python -m pip install -e . -c /home/tseaver/projects/agendaless/Google/src/python-bigtable/testing/constraints-3.8.txt
nox > py.test --quiet --junitxml=system_3.8_sponge_log.xml tests/system -x
E
==================================== ERRORS ====================================
_____________ ERROR at setup of test_table_read_rows_filter_millis _____________

    @pytest.fixture(scope="session")
    def admin_client():
>       return Client(admin=True)

tests/system/conftest.py:76: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
google/cloud/bigtable/client.py:184: in __init__
    super(Client, self).__init__(
.nox/system_emulated/lib/python3.8/site-packages/google/cloud/client.py:316: in __init__
    _ClientProjectMixin.__init__(self, project=project, credentials=credentials)
.nox/system_emulated/lib/python3.8/site-packages/google/cloud/client.py:264: in __init__
    project = self._determine_default(project)
.nox/system_emulated/lib/python3.8/site-packages/google/cloud/client.py:283: in _determine_default
    return _determine_default_project(project)
.nox/system_emulated/lib/python3.8/site-packages/google/cloud/_helpers.py:152: in _determine_default_project
    _, project = google.auth.default()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

scopes = None, request = None, quota_project_id = None, default_scopes = None

    def default(scopes=None, request=None, quota_project_id=None, default_scopes=None):
        """Gets the default credentials for the current environment.
    
        `Application Default Credentials`_ provides an easy way to obtain
        credentials to call Google APIs for server-to-server or local applications.
        This function acquires credentials from the environment in the following
        order:
    
        1. If the environment variable ``GOOGLE_APPLICATION_CREDENTIALS`` is set
           to the path of a valid service account JSON private key file, then it is
           loaded and returned. The project ID returned is the project ID defined
           in the service account file if available (some older files do not
           contain project ID information).
    
           If the environment variable is set to the path of a valid external
           account JSON configuration file (workload identity federation), then the
           configuration file is used to determine and retrieve the external
           credentials from the current environment (AWS, Azure, etc).
           These will then be exchanged for Google access tokens via the Google STS
           endpoint.
           The project ID returned in this case is the one corresponding to the
           underlying workload identity pool resource if determinable.
        2. If the `Google Cloud SDK`_ is installed and has application default
           credentials set they are loaded and returned.
    
           To enable application default credentials with the Cloud SDK run::
    
                gcloud auth application-default login
    
           If the Cloud SDK has an active project, the project ID is returned. The
           active project can be set using::
    
                gcloud config set project
    
        3. If the application is running in the `App Engine standard environment`_
           (first generation) then the credentials and project ID from the
           `App Identity Service`_ are used.
        4. If the application is running in `Compute Engine`_ or `Cloud Run`_ or
           the `App Engine flexible environment`_ or the `App Engine standard
           environment`_ (second generation) then the credentials and project ID
           are obtained from the `Metadata Service`_.
        5. If no credentials are found,
           :class:`~google.auth.exceptions.DefaultCredentialsError` will be raised.
    
        .. _Application Default Credentials: https://developers.google.com\
                /identity/protocols/application-default-credentials
        .. _Google Cloud SDK: https://cloud.google.com/sdk
        .. _App Engine standard environment: https://cloud.google.com/appengine
        .. _App Identity Service: https://cloud.google.com/appengine/docs/python\
                /appidentity/
        .. _Compute Engine: https://cloud.google.com/compute
        .. _App Engine flexible environment: https://cloud.google.com\
                /appengine/flexible
        .. _Metadata Service: https://cloud.google.com/compute/docs\
                /storing-retrieving-metadata
        .. _Cloud Run: https://cloud.google.com/run
    
        Example::
    
            import google.auth
    
            credentials, project_id = google.auth.default()
    
        Args:
            scopes (Sequence[str]): The list of scopes for the credentials. If
                specified, the credentials will automatically be scoped if
                necessary.
            request (Optional[google.auth.transport.Request]): An object used to make
                HTTP requests. This is used to either detect whether the application
                is running on Compute Engine or to determine the associated project
                ID for a workload identity pool resource (external account
                credentials). If not specified, then it will either use the standard
                library http client to make requests for Compute Engine credentials
                or a google.auth.transport.requests.Request client for external
                account credentials.
            quota_project_id (Optional[str]): The project ID used for
                quota and billing.
            default_scopes (Optional[Sequence[str]]): Default scopes passed by a
                Google client library. Use 'scopes' for user-defined scopes.
        Returns:
            Tuple[~google.auth.credentials.Credentials, Optional[str]]:
                the current environment's credentials and project ID. Project ID
                may be None, which indicates that the Project ID could not be
                ascertained from the environment.
    
        Raises:
            ~google.auth.exceptions.DefaultCredentialsError:
                If no credentials were found, or if the credentials found were
                invalid.
        """
        from google.auth.credentials import with_scopes_if_required
    
        explicit_project_id = os.environ.get(
            environment_vars.PROJECT, os.environ.get(environment_vars.LEGACY_PROJECT)
        )
    
        checkers = (
            # Avoid passing scopes here to prevent passing scopes to user credentials.
            # with_scopes_if_required() below will ensure scopes/default scopes are
            # safely set on the returned credentials since requires_scopes will
            # guard against setting scopes on user credentials.
            lambda: _get_explicit_environ_credentials(quota_project_id=quota_project_id),
            lambda: _get_gcloud_sdk_credentials(quota_project_id=quota_project_id),
            _get_gae_credentials,
            lambda: _get_gce_credentials(request),
        )
    
        for checker in checkers:
            credentials, project_id = checker()
            if credentials is not None:
                credentials = with_scopes_if_required(
                    credentials, scopes, default_scopes=default_scopes
                )
    
                # For external account credentials, scopes are required to determine
                # the project ID. Try to get the project ID again if not yet
                # determined.
                if not project_id and callable(
                    getattr(credentials, "get_project_id", None)
                ):
                    if request is None:
                        request = google.auth.transport.requests.Request()
                    project_id = credentials.get_project_id(request=request)
    
                if quota_project_id:
                    credentials = credentials.with_quota_project(quota_project_id)
    
                effective_project_id = explicit_project_id or project_id
                if not effective_project_id:
                    _LOGGER.warning(
                        "No project ID could be determined. Consider running "
                        "`gcloud config set project` or setting the %s "
                        "environment variable",
                        environment_vars.PROJECT,
                    )
                return credentials, effective_project_id
    
>       raise exceptions.DefaultCredentialsError(_HELP_MESSAGE)
E       google.auth.exceptions.DefaultCredentialsError: Could not automatically determine credentials. Please set GOOGLE_APPLICATION_CREDENTIALS or explicitly create credentials and re-run the application. For more information, please see https://cloud.google.com/docs/authentication/getting-started

.nox/system_emulated/lib/python3.8/site-packages/google/auth/_default.py:488: DefaultCredentialsError
------------------------------ Captured log setup ------------------------------
WARNING  google.auth.compute_engine._metadata:_metadata.py:97 Compute Engine Metadata server unavailable on attempt 1 of 3. Reason: timed out
WARNING  google.auth.compute_engine._metadata:_metadata.py:97 Compute Engine Metadata server unavailable on attempt 2 of 3. Reason: [Errno 113] No route to host
WARNING  google.auth.compute_engine._metadata:_metadata.py:97 Compute Engine Metadata server unavailable on attempt 3 of 3. Reason: timed out
WARNING  google.auth._default:_default.py:286 Authentication failed using Compute Engine authentication due to unavailable metadata server.
- generated xml file: /home/tseaver/projects/agendaless/Google/src/python-bigtable/system_3.8_sponge_log.xml -
=========================== short test summary info ============================
ERROR tests/system/test_data_api.py::test_table_read_rows_filter_millis - goo...
!!!!!!!!!!!!!!!!!!!!!!!!!! stopping after 1 failures !!!!!!!!!!!!!!!!!!!!!!!!!!!
1 error in 6.18s
nox > Command py.test --quiet --junitxml=system_3.8_sponge_log.xml tests/system -x failed with exit code 1
nox > Session system_emulated failed.