Recently on working hadoop (version 2.5.1) cluster we got this issue while starting ZookeepreFailOverController(zkfc).
After debugging we found its due to missing/corrupted parent znode in zookeepre cluster.
This fix this we have used following command:
$ bin/hdfs zkfc -formatZK
We ran this command before starting hdfs.
After formating, zkfc started and everything started working smoothly.