Upgrade gcloud dependency to latest version of google-cloud

### What

Upgrade `gcloud` dependency to latest version of `google-cloud` (currently `0.20.x`).
### Why
1. Dependency issues: See https://github.com/googleapis/artman/issues/102 for context.
2. Stop using Logging v1, which is deprecated.
