Merge branch 'stable-3.4' into stable-3.5

* stable-3.4:
  Do not rely on async/wait for synchronous fetch replication
  Cover the replication failure scenario and fix the metrics
  Remove white-box unit tests on synchronous FetchCommand
  Throw Exception from tests

Change-Id: If6d8c34f65d4c88d77d062f466b1163b215f806e