Using absolute imports in core modules that import grpc.

[dhermes]

This is because a relative import (in Python 2.7) was causing failures when google.cloud.grpc was side-by-side with google.cloud._helpers, etc.

For example, see the failure: https://travis-ci.org/GoogleCloudPlatform/google-cloud-python/builds/171149390#L1738-L1750

FYI @geigerj @bjwatson

To repro (before this PR):

$ cd ${GIT_ROOT}
$ tox -e system-tests --recreate --notest
$ source .tox/system-tests/bin/activate
$ .tox/system-tests/bin/py.test system_tests/datastore.py --pdb
...
>       transport_creds = grpc.ssl_channel_credentials()
E       AttributeError: 'module' object has no attribute 'ssl_channel_credentials'

.tox/system-tests/local/lib/python2.7/site-packages/google/cloud/_helpers.py:643: AttributeError
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> entering PDB >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> .tox/system-tests/local/lib/python2.7/site-packages/google/cloud/_helpers.py(643)make_secure_stub()
-> transport_creds = grpc.ssl_channel_credentials()
(Pdb) grpc
<module 'google.cloud.grpc' (built-in)>
(Pdb) 

[dhermes]

@bjwatson ISTM that in later generations of GAPIC generated code the google.cloud.grpc package is gone. Is this correct?

i.e. it is brought in by the speech deps (uploaded on sept. 30)

https://pypi.python.org/pypi/grpc-google-cloud-speech-v1beta1/0.11.1
https://pypi.python.org/pypi/gapic-google-cloud-speech-v1beta1/0.11.1

[dhermes]

Chatted @bjwatson, he confirmed that google.cloud.grpc is here to stay. For packages like speech where the namespace is google.cloud.speech.v1beta1, putting the autogenerated packages in google.cloud.speech.v1beta1.cloud_speech_pb would cause a collision with our package google.cloud.speech (which isn't a namespace package) so the autogenerated are instead in google.cloud.grpc.speech.v1beta1.cloud_speech_pb

/FYI @jonparrott

[theacodes]

Yep - remember having that discussion a while back. SGTM.