Merge branch 'stable-3.7' into stable-3.8

* stable-3.7:
  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: Ia2e8d8900374611b3e67ab526688681e32152742