Merge branch 'stable-3.1'

* stable-3.1:
  Bump Bazel version to 2.0.0

PutOwner: Adapt to recent master change I295c8679. Use string
concatenation, consistently with other concatenations in that file.
Stick to plugin release API for standalone though, as this adaptation
fits the Exception type constructor hierarchy.

Change-Id: Ia224cd453453b75807fe2edf5b22c21dd37fbb6e