message: Point tpu_cluster_resolver.py to the v1 TPU API.
  The v1 API is available. It might be good to consider allowing customers to pick which API version they want, but for now use the v1 API.
diff: @@ -109,11 +109,11 @@ class TPUClusterResolver(ClusterResolver):
  if self._discovery_url:
  return discovery.build(
  - 'tpu', 'v1alpha1', credentials=credentials,
  + 'tpu', 'v1', credentials=credentials,
  discoveryServiceUrl=self._discovery_url, cache_discovery=False)
  else:
  return discovery.build(
  - 'tpu', 'v1alpha1', credentials=credentials, cache_discovery=False)
  + 'tpu', 'v1', credentials=credentials, cache_discovery=False)
  def _request_compute_metadata(self, path):
  req = Request('%s/computeMetadata/v1/%s' % (_GCE_METADATA_ENDPOINT, path),
  