Add IAM support to APIs which support it #1679
Description
(copied from googleapis/google-cloud-node#1192, which is funnily-enough exactly true for gcloud-python, too).
IAM is currently buried inside of our Pub/Sub code, but should be abstracted to be used with any API that supports it:
- BigQuery
- Compute
- Logging
- Pub/Sub
- Resource Manager
- Storage