public AsyncClusterConnection getAsyncConnection(User user) throws IOException {
    return ClusterConnectionFactory.createAsyncClusterConnection(conf, null, user);
  }
Get a assigned AsyncClusterConnection to the cluster. this method is thread safe.
@param user assigned user
@return An AsyncClusterConnection with assigned user.
hbase-server/src/test/java/org/apache/hadoop/hbase/HBaseTestingUtil.java