public void sync(String path, AsyncCallback.VoidCallback cb, Object ctx) throws KeeperException {
    checkZk().sync(path, cb, ctx);
  }
Returns the wrapped ZooKeeper client. If the wrapped client hasn't been created yet then tries
create it first.
@return the wrapped ZK client of null if the creation has failed.
hbase-zookeeper/src/main/java/org/apache/hadoop/hbase/zookeeper/RecoverableZooKeeper.java