boolean deleteOnExit() {
    String v = System.getProperty("hbase.testing.preserve.testdir");
    // Let default be true, to delete on exit.
    return v == null ? true : !Boolean.parseBoolean(v);
  }
Returns True if we should delete testing dirs on exit.
hbase-testing-util/src/main/java/org/apache/hadoop/hbase/HBaseCommonTestingUtility.java