Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Upgrade bazlets to latest stable-2.15 to build with 2.15.19 API
  Upgrade bazlets to latest stable-2.14 to build with 2.14.21 API

Change-Id: I7119ae15a234e72abb86a46eb2075a4c7fb57c01