Merge branch 'stable-3.1'

* stable-3.1:
  Bump Bazel version to 3.0.0
  Upgrade bazlets to latest stable-2.16 to build with 2.16.17 API
  Upgrade bazlets to latest stable-2.16

Change-Id: If6898ee2569cba6a489fc6fb2d30d2b426c85368