Merge branch 'stable-3.1'

* stable-3.1:
  Upgrade bazlets to latest stable-3.1 to build with 3.1.7 API
  Upgrade bazlets to latest stable-3.0 to build with 3.0.11 API
  Remove the commented-out snapshot plugin api lines
  Adapt SNAPSHOT plugin api example to the 3.1 version
  Upgrade bazlets to latest stable-3.1
  Upgrade bazlets to latest stable-3.0
  Clean-up definition of gerrit API jars
  Upgrade bazlets to latest stable-3.0

Change-Id: I055208581eccf504bff76ca34ad348fb628d09e1