Merge branch 'stable-3.0'

* stable-3.0:
  Upgrade bazlets to latest master to build with 3.0.0-rc2 API
  Upgrade bazlets to latest stable-2.16 to build with 2.16.8 API
  Upgrade bazlets to latest stable-2.15 to build with 2.15.13 API

Switch from release to snapshot plugin API use, since this is master
branch anyway. Without this switch, some of the plugin test code failed
to build locally, out of missing BranchNameKey.

Change-Id: Ic2318aab808f252a854ba03d9c753bffb6785201