Merge branch 'stable-2.16' into stable-3.0

* stable-2.16:
  Bump bazel version to 1.0.0
  Add PolyGerrit UI for configuring uploadvalidator
  Upgrade bazlets to latest stable-2.16 to build with 2.16.12 API
  Upgrade bazlets to latest stable-2.15 to build with 2.15.17 API

Change-Id: I40633e357b1fe9c579ede32a1039042830c1f612