private static HRegionServer getRS() {
    return HTU.getHBaseCluster().getLiveRegionServerThreads().get(0).getRegionServer();
  }
Flush the given region in the mini cluster. Since no master, we cannot use HBaseAdmin.flush()
hbase-server/src/test/java/org/apache/hadoop/hbase/regionserver/TestRegionServerNoMaster.java