Merge branch 'stable-3.1'

* stable-3.1:
  Update subscriber metrics at every replication stage
  Enable HTTP log in test environment
  Add and configure Prometheus with the multi-site environment
  Fix typo in setup.sh messages
  Dry out Gerrit CI URL in setup.sh script
  Tidy up replication lag metrics publishing logs
  Fix replication lag unit: seconds
  SubscriberMetrics: update only when replication is complete
  Store version value in shared db

Change-Id: I2035133401508ccfdf72e2e88ca4c474327eccb6