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: I2c92be0bd9feb0cab21bf56df9f973fa08137fc0