Improve ZooKeeper-relevant code

Including variable naming and locations, code format, config options,
ZooKeeper data paths, logging level, and other design issues, etc.

Inception SDN controller has *basic* high availability now, which can
stand controller restart, controller fail-over, in the presence of no
ongoing network events or operations.
Merge pull request #23 from changbl/working

Improve ZooKeeper-relevant code