Added configuration options for ZooKeeper username & password for heartbeat management. Also addressed issue where nodes that were previously disconnected were asked to disconnect upon restart
Ensure that ACL is set properly when creating heartbeat node. Removed unused ControllerStartupFailureMessage.java
Changed ZooKeeper ACL's so that container nodes that would not be sensitive are wide open and removed the usage of username & password when communicating with ZooKeeper. This was done specifically because username/password combination is considered a 'testing' feature that should not be used in production and is not supported by Apache Curator
Refactored CuratorHeartbeatMonitor into an abstract heartbeat monitor that is responsible for processing heartbeats and CuratorHeartbeatMonitor that is responsible for retrieving heartbeat information
Refactored so that heartbeats are sent to Cluster Coordinator directly instead of to ZooKeeper. ZooKeeper is used to know which node is the cluster coordinator but heartbeats to the Cluster Coordinator provide additional information about the nodes.
Code cleanup and incorporate comments from peer review
This closes#323
