Adding support for debug logs in executed functions.

[vrdmr]

Description

Changing the default log level to Debug. The configuration of the log levels is set at the host.json.

FYI @stefanushinardi @anthonychu

Fixes #735

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[Hazhzeng]

I remember @ankitkumarr and I once dealt with a CRI where a customer's application performance got impacted due to too many logs from azure-storage-blob.

Since we're now enabling debug in Python in the root logger, I expect to see a bit more logger.debug from azure-storage-blob. (e.g. https://github.com/Azure/azure-storage-python/blob/4e03ff8c9d6c76a38666a8ceb8937593e93fb7eb/azure-storage-common/azure/storage/common/_auth.py#L93.)

I think it would be great if you can create some test cases with a host.json that controls the log level, and see if the host actually filters our worker logs.
https://docs.microsoft.com/en-us/azure/azure-functions/functions-host-json#sample-hostjson-file

    "logging": {
        "logLevel": {
          "Function.MyFunction": "Information",
          "default": "None"
        }

Currently, the Python worker tests all use host.json from testutils.py -> HOST_JSON_TEMPLATE. When the test starts, it will copy the content to each unittest folder's root (e.g. tests/unittests/http_functions/host.json) in testsutils.py -> _setup_func_app. If not taking too much time, you can create a new test instance to modify the host.json context before starting the test host. Let me know if you have any questions.

[vrdmr]

I think it would be great if you can create some test cases with a host.json that controls the log level, and see if the host actually filters our worker logs.
https://docs.microsoft.com/en-us/azure/azure-functions/functions-host-json#sample-hostjson-file

Done - added a new set of tests with Information log level (default) set to confirm debug logs are not sent.

[Hazhzeng]

[Hazhzeng]

Great, this explicitly test the scenario on the host logging control side. Thanks for making the change