gRPC pubsub missing scope error #2908
Description
It appears that something changed in gRPC.
Exception google.auth.exceptions.RefreshError: RefreshError('invalid_scope: Empty or missing scope not allowed.', u'{\n "error" : "invalid_scope",\n "error_description" : "Empty or missing scope not allowed."\n}') in 'grpc._cython.cygrpc.plugin_get_metadata' ignored
Reference: https://travis-ci.org/GoogleCloudPlatform/google-cloud-python/builds/187483537#L2101
Running $ tox -e system-tests -- pubsub yields the same results.
However running $ GOOGLE_CLOUD_DISABLE_GRPC=true tox -e system-tests -- pubsub allows the tests to pass.