Merge branch 'stable-2.15'

* stable-2.15:
  Upgrade bazlets to latest stable-2.15 to build with 2.15.7 API
  Upgrade bazlets to latest stable-2.14 to build with 2.14.17 API

Change-Id: I50a69462730e7f86a73e04a1ef5cf2bf37c19c9a