update Google Cloud API client import paths and more

[jba]

The Google Cloud API client libraries for Go are making some breaking changes:

• The import paths are changing from google.golang.org/cloud/... to
  cloud.google.com/go/.... For example, if your code imports the BigQuery client
  it currently reads
  import "google.golang.org/cloud/bigquery"
  It should be changed to
  import "cloud.google.com/go/bigquery"
• Client options are also moving, from google.golang.org/cloud to
  google.golang.org/api/option. Two have also been renamed:
  • WithBaseGRPC is now WithGRPCConn
  • WithBaseHTTP is now WithHTTPClient
• The cloud.WithContext and cloud.NewContext methods are gone, as are the
  deprecated pubsub and container functions that required them. Use the Client
  methods of these packages instead.

You should make these changes before September 12, 2016, when the packages at
google.golang.org/cloud will go away.