void shutdown() {
      stopped = true;
      interrupt();
    }
Start a minidfscluster. Can only create one.
@param servers How many DNs to start.
@param hosts   hostnames DNs to run on.
@see #shutdownMiniDFSCluster()
@return The mini dfs cluster created.
hbase-server/src/test/java/org/apache/hadoop/hbase/HBaseTestingUtil.java