Merge pull request #101 from changbl/working

Remove Topology.dpid_to_dpid
Failover with zookeeper

This version has normal functionality
and basic failover without queue.

1. Failover for packet_in handling
2. Failover for RPC
3. Fix bugs introduced by previous commit
Merge pull request #102 from powerist/failover

Failover with zookeeper
Seamless HA

1. New leader election
2. Seamless controller failover
Merge pull request #103 from powerist/leaderele

Seamless High Availability (HA with queue)
Merge load_failover_logs and handle_failover_log
Merge pull request #106 from powerist/leaderele

Merge load_failover_logs and handle_failover_log
Add timestamp to inception_arp eval and minor to logging