Merge branch 'stable-3.1' into stable-3.2

* stable-3.1:
  Elasticsearch: Remove support for EOL 6.7 version
  Update the recommended buildifier version to 3.5.0
  Remove unused Documentation/config-login-register.txt

Change-Id: I6e647f810447675316ee83e0cd2a50e4da61b511
tree: 61b55419c5fa7c3b60f386e063714a64f71f5ce7
  1. java/
  2. javatests/