@Override
      public int compare(String o1, String o2) {
        // jm version name format is <num>
        return Integer.valueOf(o1) - Integer.valueOf(o2);
      }
cleanup old data from ZK
@param numVersionsToLeave - number of versions to leave
samza-core/src/main/java/org/apache/samza/zk/ZkUtils.java