Merge branch 'stable-3.0' into stable-3.1

* stable-3.0:
  Use Gerrit 3.0.12 in Dockerfile
  Upgrade bazlets to latest stable-3.0 to build with 3.0.12 API
  Use Gerrit 2.16.22 in Dockerfile
  Upgrade bazlets to latest stable-2.16 to build with 2.16.22 API

Change-Id: I948afe32f8cc46b4b7a7d1511d94e87df38d1d83