public JVMClusterUtil.RegionServerThread stopRegionServer(int serverNumber) {
    return stopRegionServer(serverNumber, true);
  }
Shut down the specified region server cleanly
@param serverNumber Used as index into a list.
@return the region server that was stopped
hbase-testing-util/src/main/java/org/apache/hadoop/hbase/MiniHBaseCluster.java