Merge branch 'stable-3.1'

* stable-3.1:
  Upgrade bazlets to latest stable-3.1 to build with 3.1.8 API
  Move plugin configuration to a separate file
  Upgrade bazlets to latest stable-3.0 to build with 3.0.12 API
  Upgrade bazlets to latest stable-2.16 to build with 2.16.22 API

Change-Id: Ic4e5b3bb816673183fc5dc8542546fb6936c19a8