Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  Set Gerrit to 2.15.18
  Set Gerrit to 2.15.17
  Set Gerrit to 2.15.16
  Set Gerrit to 2.15.15
  Set Gerrit to 2.15.14

Change-Id: I90ad6b18c008666497db364ee6f2535f1f2ec76d