[DO NOT MERGE] Bigtable: pick up fixes in GAPIC generator.

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Cloning googleapis.
synthtool > Running generator for google/bigtable/artman_bigtable.yaml.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:90f9d15e9bad675aeecd586725bce48f5667ffe7d5fc4d1e96d51ff34304815b
Status: Image is up to date for googleapis/artman:latest
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigtable-v2.
synthtool > Running generator for google/bigtable/admin/artman_bigtableadmin.yaml.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:90f9d15e9bad675aeecd586725bce48f5667ffe7d5fc4d1e96d51ff34304815b
Status: Image is up to date for googleapis/artman:latest
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/bigtable-admin-v2.
synthtool > Replaced "'google-cloud-bigtable-admin'" in google/cloud/bigtable_admin_v2/gapic/bigtable_instance_admin_client.py.
synthtool > Replaced "'google-cloud-bigtable-admin'" in google/cloud/bigtable_admin_v2/gapic/bigtable_table_admin_client.py.
synthtool > Replaced 'from google\\.cloud\\.bigtable\\.admin_v2.proto' in google/cloud/bigtable_admin_v2/proto/bigtable_table_admin_pb2_grpc.py.
synthtool > Replaced 'from google\\.cloud\\.bigtable\\.admin_v2.proto' in google/cloud/bigtable_admin_v2/proto/bigtable_table_admin_pb2.py.
synthtool > Replaced 'from google\\.cloud\\.bigtable\\.admin_v2.proto' in google/cloud/bigtable_admin_v2/proto/instance_pb2.py.
synthtool > Replaced 'from google\\.cloud\\.bigtable\\.admin_v2.proto' in google/cloud/bigtable_admin_v2/proto/bigtable_instance_admin_pb2.py.
synthtool > Replaced 'from google\\.cloud\\.bigtable\\.admin_v2.proto' in google/cloud/bigtable_admin_v2/proto/bigtable_instance_admin_pb2_grpc.py.
synthtool > Replaced 'google.api_core.grpc_helpers.create_channel\\(\n(\\s+)address.*\n\\s+credentials.*\n\\s+scopes.*\n' in google/cloud/bigtable_admin_v2/gapic/transports/bigtable_table_admin_grpc_transport.py.
synthtool > Replaced 'google.api_core.grpc_helpers.create_channel\\(\n(\\s+)address.*\n\\s+credentials.*\n\\s+scopes.*\n' in google/cloud/bigtable_v2/gapic/transports/bigtable_grpc_transport.py.
synthtool > Replaced '    __doc__ = bigtable_instance_admin_client.BigtableInstanceAdminClient.__doc__\n' in google/cloud/bigtable_admin_v2/__init__.py.
synthtool > Cleaned up 0 temporary directories.

[tseaver]

Codegen is busted:

  File "/var/code/gcp/bigtable/google/cloud/bigtable/__init__.py", line 21, in <module>
    from google.cloud.bigtable.client import Client
  File "/var/code/gcp/bigtable/google/cloud/bigtable/client.py", line 40, in <module>
    from google.cloud.bigtable.instance import Instance
  File "/var/code/gcp/bigtable/google/cloud/bigtable/instance.py", line 20, in <module>
    from google.cloud.bigtable.table import Table
  File "/var/code/gcp/bigtable/google/cloud/bigtable/table.py", line 37, in <module>
    from google.cloud.bigtable import enums
  File "/var/code/gcp/bigtable/google/cloud/bigtable/enums.py", line 19, in <module>
    class StorageType(object):
  File "/var/code/gcp/bigtable/google/cloud/bigtable/enums.py", line 28, in StorageType
    UNSPECIFIED = enums.StorageType.STORAGE_TYPE_UNSPECIFIED
AttributeError: module 'google.cloud.bigtable_admin_v2.gapic.enums' has no attribute 'StorageType'

[tseaver]

I verified the breakage locally. See googleapis/gapic-generator#2429.

[andreamlin]

Hmm, this might have been my breakage: googleapis/gapic-generator#2441

[andreamlin]

We're planning on having artman smoketests run on gapic-generator check-ins so that we don't have these kinda breakages down the road. (ex googleapis/gapic-generator#2443)

[tseaver]

Superseded by #6630.