Merge branch 'stable-3.1'

* stable-3.1:
  Set Gerrit to 3.1.6
  Set Gerrit to 3.0.10
  Set Gerrit to 2.16.21
  Set Gerrit to 2.15.19
  Set Gerrit to 2.14.21
  Set version to 2.16.20
  Set Gerrit to 3.1.5
  Set Gerrit to 3.0.9
  Set version to 2.16.19
  Set version to 2.16.18

Change-Id: Ia3a7a42e98bc0a2e36425b301720767ca189727f