Merge branch 'stable-3.0' into stable-3.1

* stable-3.0:
  Elasticsearch: Remove support for EOL 6.7 version
  Update the recommended buildifier version to 3.5.0
  Remove unused Documentation/config-login-register.txt

From this branch, the downstream dev-contributing.txt content moved to
dev-crafting-changes.txt.

Change-Id: I2578843a42f29e09f90ee2918bd5206e3dd273db
tree: 2a8c3d436f9c9748e83a254b2704a02fa8f34a5d
  1. java/
  2. javatests/