Swarming: Patches Auth default credentials at startup

[IvanBM18]

Fuzzing tasks ins warming have an intermittent error in which startup of any gcp lirbary or module fails with:

  File "/mnt/scratch0/clusterfuzz/src/clusterfuzz/_internal/datastore/ndb_init.py", line 39, in _client
    _ndb_client = ndb.Client(project=utils.get_application_id())
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/cloud/ndb/client.py", line 145, in __init__
    super(Client, self).__init__(
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/cloud/client/__init__.py", line 320, in __init__
    _ClientProjectMixin.__init__(self, project=project, credentials=credentials)
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/cloud/client/__init__.py", line 268, in __init__
    project = self._determine_default(project)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/cloud/ndb/client.py", line 249, in _determine_default
    return _determine_default_project(project)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/cloud/ndb/client.py", line 70, in _determine_default_project
    project = _helpers._determine_default_project(project=project)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/cloud/_helpers/__init__.py", line 152, in _determine_default_project
    _, project = google.auth.default()
                 ^^^^^^^^^^^^^^^^^^^^^
  File "/mnt/scratch0/clusterfuzz/src/third_party/google/auth/_default.py", line 692, in default
    raise exceptions.DefaultCredentialsError(_CLOUD_SDK_MISSING_CREDENTIALS)
google.auth.exceptions.DefaultCredentialsError: Your default credentials were not found. To set up Application Default Credentials, see https://cloud.google.com/docs/authentication/external/set-up-adc for more information.

This happens because the timeout for calling the default credentials times out because credentials coming from luci-auth doesn't always comes fast enough for the internal gcp libraries.

To fix this, we are manually patching the google.auth.default module to return some credentials that do come from the swarming bot.

Note: This is a draft since dev testing is still in progress, will open the PR when dev testing is finished.

[IvanBM18]

Note: We have the args and kwargs in the method signature because otherwise if we call the default() method with any args an exception would be thrown because the patch didn't matched the expected signature.