Merge branch 'stable-3.0' into stable-3.1

* stable-3.0:
  Set Gerrit to 3.0.10
  Set Gerrit to 2.16.21
  Set Gerrit to 2.15.19
  Fetch plugins from archive-ci.gerritforge.com
  Set Gerrit to 2.14.21
  Set version to 2.16.20

Change-Id: Iaeb6d7d2e4d51a560b80483320f4ebd1cc8a2ec9