Merge branch 'stable-3.1'

* stable-3.1:
  Update Gerrit API to 3.1.5
  Update Gerrit API to 3.0.9
  Update Gerrit API to 2.16.19
  Update Gerrit API to 2.16.18

Change-Id: I968e5ccac8dd737409bde131af118d373471d519