Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Set Gerrit to 2.15.10
  Set Gerrit to 2.15.9
  Set Gerrit to 2.13.12
  Set Gerrit to 2.14.18
  Set Gerrit to 2.15.8
  Set Gerrit to 2.15.7
  Set Gerrit to 2.14.17
  Set Gerrit to 2.15.6
  Set Gerrit to 2.14.16
  Upgrade CentOS to 7.5.1804
  Add support for Gerrit 2.13.11 on ubuntu 14.04 and centos

Change-Id: Ia821612383f163417f2dfd8c91977e909509616a