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
  Bazel: Migrate workspace status script to python
  Upgrade bazlets to latest stable-2.15
  Upgrade bazlets to latest stable-2.14

Change-Id: I7c5dafd1978e0bd348006b2cfd67cc7b061bdae5