feat(container): add 'list_usable_subnetworks' method; apply proto annotations (via synth)

[yoshi-automation]

This PR was generated using Autosynth. 🌈

Log from Synthtool

synthtool > Executing /tmpfs/src/git/autosynth/working_repo/container/synth.py.
synthtool > Ensuring dependencies.
synthtool > Pulling artman image.
latest: Pulling from googleapis/artman
Digest: sha256:545c758c76c3f779037aa259023ec3d1ef2d57d2c8cd00a222cb187d63ceac5e
Status: Image is up to date for googleapis/artman:latest
synthtool > Cloning googleapis.
synthtool > Running generator for google/container/artman_container_v1beta1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/container-v1beta1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/container/v1beta1/cluster_service.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/container-v1beta1/google/cloud/container_v1beta1/proto/cluster_service.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/container-v1beta1/google/cloud/container_v1beta1/proto.
synthtool > Running generator for google/container/artman_container_v1.yaml.
synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/container-v1.
synthtool > Copy: /home/kbuilder/.cache/synthtool/googleapis/google/container/v1/cluster_service.proto to /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/container-v1/google/cloud/container_v1/proto/cluster_service.proto
synthtool > Placed proto files into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/container-v1/google/cloud/container_v1/proto.
synthtool > Replaced '(^.*$\\n)*' in google/cloud/container_v1beta1/proto/cluster_service_pb2.py.
synthtool > Replaced '(^.*$\\n)*' in google/cloud/container_v1/proto/cluster_service_pb2.py.
synthtool > No replacements made in google/**/proto/cluster_service_pb2.py for pattern nodePool>\n, maybe replacement is not longer needed?
synthtool > No replacements made in google/**/proto/cluster_service_pb2.py for pattern (\s+)`__ instead, maybe replacement is not longer needed?
.coveragerc
.flake8
MANIFEST.in
docs/_static/custom.css
docs/_templates/layout.html
noxfile.py.j2
setup.cfg
Running session blacken
Creating virtual environment (virtualenv) using python3.6 in .nox/blacken
pip install black==19.3b0
black docs google tests noxfile.py setup.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/gapic/transports/cluster_manager_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/gapic/cluster_manager_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/types.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/__init__.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/proto/cluster_service_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/gapic/cluster_manager_client_config.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/gapic/enums.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/gapic/transports/cluster_manager_grpc_transport.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/gapic/cluster_manager_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/gapic/cluster_manager_client.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/types.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/proto/cluster_service_pb2_grpc.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/noxfile.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/tests/unit/gapic/v1/test_cluster_manager_client_v1.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/tests/unit/gapic/v1beta1/test_cluster_manager_client_v1beta1.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1beta1/proto/cluster_service_pb2.py
reformatted /tmpfs/src/git/autosynth/working_repo/container/google/cloud/container_v1/proto/cluster_service_pb2.py
All done! ✨ 🍰 ✨
20 files reformatted, 11 files left unchanged.
Session blacken was successful.
synthtool > Cleaned up 2 temporary directories.
synthtool > Wrote metadata to synth.metadata.