private int randomPort() {
      return MIN_RANDOM_PORT
        + ThreadLocalRandom.current().nextInt(MAX_RANDOM_PORT - MIN_RANDOM_PORT);
    }
Returns a random port. These ports cannot be registered with IANA and are intended for
dynamic allocation (see http://bit.ly/dynports).
hbase-testing-util/src/main/java/org/apache/hadoop/hbase/HBaseCommonTestingUtility.java