Add timeout for cluster termination

Currently, cluster termination may be blocked forever as there's no timeout for that. For example, for an Application cluster with ZK HA enabled, when ZK cluster is down, the cluster will reach termination status, but the termination process will be blocked when trying to clean up HA data on ZK, where the ZK client will retry connecting to ZK forever. Similar phenomenon can be observed when an HDFS outage occurs.

I propose adding a timeout for the cluster termination process in ClusterEntryPoint#
shutDownAsync method.