Merge branch 'stable-3.1'

* stable-3.1:
  Bump Bazel version to 2.0.0

Adapt to recent com.google.gerrit.acceptance{.config} package change.
Use latest bazlets but switch to snapshot API for standalone, as that
package change is not in a release yet.

Change-Id: Ia7b02b4652461cc971092b9b8db8683f1a1eed1b