Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Upgrade bazlets to latest stable-2.15 to build with 2.15.16 API
  Upgrade bazlets to latest stable-2.15 to build with 2.15.15 API

Change-Id: Icd6126b029295f1ed317af5e1ae834a37708a5b6