@Override
  public String getRegionServerVersion(ServerName sn) {
    // Will return "0.0.0" if the server is not online to prevent move system region to unknown
    // version RS.
    return this.serverManager.getVersion(sn);
  }
Returns timestamp in millis when HMaster finished becoming the active master
hbase-server/src/main/java/org/apache/hadoop/hbase/master/HMaster.java