This resurrects the previously documented but unused "project" option.
This option is required to create buckets (so they are associated with the
right cloud project) but not to access the buckets later on (because their
names are globally unique).
The code is loosely based on state/remote/gcs_test.go. If the
GOOGLE_PROJECT environment variable is set, this test will
1) create a new bucket; error out if the bucket already exists.
2) create a new state
3) list states and ensure that the newly created state is listed
4) ensure that an object with the expected name exists
5) rum "state/remote".TestClient()
6) delete the state
The bucket is deleted when the test exits, though this may fail if the
bucket it not empty.