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
Prepare for new gerrit_api snapshot version usage
Upgrade bazlets to latest stable-3.0
Adapt to changed signature of apply(...) methods
Upgrade bazlets to latest stable-3.0
Change-Id: Id24cf0dcdd25689a60781405fb6908221b739db4