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: Iab97a04c7eab5649532d1ced6595457a859747c4