Fix four bugs in StackdriverTaskHandler

[mik-laj]

Unfortunately this organization is in a bit more serious condition and I found a few bugs that prevented the use of this integration.

The commit ac943c9#diff-e7f34f73940eb52d92bb991abedc1c963431c5373c12dff739c8fb7d03e93d3aR181 changed the output type for the read method. Unfortunately, this change did not update this handler as well, so the attempt to read the entries was unsuccessful.

The flush method was missing, with the result that at times one or two of the last entries were not saved. It is worth adding that the official implementation of Stackdriver Logging Handler does not have this method either. https://github.com/googleapis/python-logging/blob/master/google/cloud/logging_v2/handlers/handlers.py

I also changed the parameters for calling the entries.list method, which I have the impression that they work better. They follow the defaults for gcloud.

Close: #13494

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[github-actions]

The Workflow run is cancelling this PR. It has some failed jobs matching ^Pylint$,^Static checks,^Build docs$,^Spell check docs$,^Backport packages$,^Provider packages,^Checks: Helm tests$,^Test OpenAPI*.

[potiuk]

Indeed... interesting way of reurning data :)

[turbaszek]

Indeed... List[Tuple[Tuple[str, List]]] 😄

[mik-laj]

Tuple[List[Tuple[Tuple[str, str]]], List[Dict[str, str]]]

[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest master at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[mik-laj]

This is another small fix. An error is generated when exiting the process, but it did not cause any errors, but only noise in the log.

========================================== 9 failed, 8 passed, 3 skipped, 7 errors in 12.91s ==========================================
[2021-01-20 19:52:29,766] {_metadata.py:104} WARNING - Compute Engine Metadata server unavailable onattempt 1 of 3. Reason: timed out
[2021-01-20 19:52:29,769] {_metadata.py:104} WARNING - Compute Engine Metadata server unavailable onattempt 2 of 3. Reason: [Errno 111] Connection refused
[2021-01-20 19:52:29,774] {_metadata.py:104} WARNING - Compute Engine Metadata server unavailable onattempt 3 of 3. Reason: [Errno 111] Connection refused
[2021-01-20 19:52:29,774] {_default.py:246} WARNING - Authentication failed using Compute Engine authentication due to unavailable metadata server.
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/usr/local/lib/python3.6/logging/__init__.py", line 1946, in shutdown
    h.close()
  File "/opt/airflow/airflow/providers/google/cloud/log/stackdriver_task_handler.py", line 345, in close
    self._transport.flush()
  File "/usr/local/lib/python3.6/site-packages/cached_property.py", line 36, in __get__
    value = obj.__dict__[self.func.__name__] = self.func(obj)
  File "/opt/airflow/airflow/providers/google/cloud/log/stackdriver_task_handler.py", line 120, in _transport
    return self.transport_type(self._client, self.name)
  File "/usr/local/lib/python3.6/site-packages/cached_property.py", line 36, in __get__
    value = obj.__dict__[self.func.__name__] = self.func(obj)
  File "/opt/airflow/airflow/providers/google/cloud/log/stackdriver_task_handler.py", line 108, in _client
    key_path=self.gcp_key_path, scopes=self.scopes, disable_logging=True
  File "/opt/airflow/airflow/providers/google/cloud/utils/credentials_provider.py", line 309, in get_credentials_and_project_id
    return _CredentialProvider(*args, **kwargs).get_credentials_and_project()
  File "/opt/airflow/airflow/providers/google/cloud/utils/credentials_provider.py", line 242, in get_credentials_and_project
    credentials, project_id = self._get_credentials_using_adc()
  File "/opt/airflow/airflow/providers/google/cloud/utils/credentials_provider.py", line 295, in _get_credentials_using_adc
    credentials, project_id = google.auth.default(scopes=self.scopes)
  File "/usr/local/lib/python3.6/site-packages/google/auth/_default.py", line 356, in default
    raise exceptions.DefaultCredentialsError(_HELP_MESSAGE)
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

[mik-laj]

Stackdriver sometimes falls into an endless loop of blank pages.

[mik-laj]

In this test, we used the StackdriverTaskHandler which tries to connect to GCP in the close() method. To avoid this, I delete the handlers manually without calling this method. Similar to: https://github.com/apache/airflow/pull/13784/files#r561283952