Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Upgrade bazlets to latest stable-2.15 to build with 2.15.18 API
  Upgrade bazlets to latest stable-2.15
  Upgrade bazlets to latest stable-2.14
  Bazel: Migrate workspace status script to python

Change-Id: Ic40d3ed72fffa1144d06fca072796b3d183ae0c2