Figure out how to support "usable auth" for gcloud-node

See https://github.com/google/google-api-nodejs-client/pull/354

Ideally we would somehow integrate this code. Maybe it means a separate google-authkit-node repository that we depend on ?

/cc @stephenplusplus @ryanseys 
