Avoid too large identifier of ZooKeeperWatcher

For each SyncConnected event, the ZooKeeperWatcher will append the session id to its identity.

During the failover of zk, the zookeeper client can connect to the zk server, but the the zk server can not serve the request, so the client will try continually, which will produce many SyncConnected events and a very large identifier of ZooKeeperWatcher in hbase log.

2014-12-22,12:38:56,296 WARN org.apache.hadoop.hbase.zookeeper.ZKUtil: master:16500-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-0x349cbb4e4a7f0ba-...

A simple patch to fix this problem.