@AfterClass
  public static void afterClass() throws Exception {
    UTIL.shutdownMiniCluster();
  }
Spark creates many instances of TableOutputFormat within a single process. We need to make sure
we can have many instances and not leak connections. This test creates a few TableOutputFormats
and shouldn't fail due to ZK connection exhaustion.
hbase-mapreduce/src/test/java/org/apache/hadoop/hbase/mapred/TestTableOutputFormatConnectionExhaust.java