Merge branch 'stable-2.15'

* stable-2.15:
  Upgrade bazlets to latest stable-2.15
  Upgrade bazlets to latest stable-2.14
  Upgrade bazlets to latest stable-2.15
  Upgrade bazlets to latest stable-2.14
  ListImportedProjects: Stop using deprecated fileTreeTraverser method
  Upgrade bazlets to latest stable-2.15
  Upgrade bazlets to latest stable-2.14
  Upgrade bazlets to latest stable-2.15 to build with 2.15.14 API
  Make transitive starlark loads explicit
  Make transitive starlark loads explicit
  Upgrade bazlets to latest stable-2.15 to build with 2.15.13 API
  Upgrade bazlets to latest stable-2.14 to build with 2.14.20 API

Change-Id: I0cca836a40ff856b2e3c293e80c4250db45e9c07