SCHEMA-384. Track clients of a Kiji instance and clients of opened Kiji tables

- ZooKeeperClient that handles ZooKeeper disconnects.
- TableLayoutMonitor providing trackers for:
 - table layout updates
 - table users (client processes).
- Update ZooKeeperLock to use ZooKeeperClient.

issue: https://jira.kiji.org/browse/SCHEMA-384
review: https://review.kiji.org/r/616