Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Upgrade bazlets to latest stable-2.15 to build with 2.15.10 API
  Upgrade JGit to 4.9.8.201812241815-r
  Upgrade JGit to 4.7.7.201812240805-r
  Upgrade bazlets to latest stable-2.15 to build with 2.15.9 API
  Upgrade bazlets to latest stable-2.15 to build with 2.15.8 API
  Upgrade bazlets to latest stable-2.14 to build with 2.14.18 API
  Bazel: Include eclipse-out directory in .bazelignore
  Add explanatory comment to empty BUILD file(s)

Change-Id: I4d60d326d7df689c351e4e9456d51fd1bb8832dc