Merge branch 'stable-2.16' into stable-3.0

* stable-2.16:
  Upgrade bazlets to latest stable-2.16 to build with 2.16.21 API
  Upgrade bazlets to latest stable-2.15 to build with 2.15.19 API

Change-Id: I9794fad4feb4d58667da18cde4c24bcb541ca3e0