Provide HA to local controller

Currently if local controller goes down then flows can not be updated on the failed controller, therefore support for HA should be provide. In case of failure of local controller there can be following ways to handle it

1) Try to bring up failed local controller using watchdog. If watchdog succeed then stop the recovery mechanism else go to step 2 to recover.
2) Transfer the control to one of the active controller and new controller will be responsible for maintaining flows on failed controller's nodes.