openflow role switch message implementation

Implement role switch message and provide initial logic to trigger the failover. To enable role switch message capability following task need to be done

• stub for entry point where propagation of role change should start
• logic for pushing role to device with failover
• role change logic wired to openflowpluginprovider
• Unit tests

This task implement all the required tooling that will be required to implement the controller failover mechanism.

https://wiki.opendaylight.org/view/OpenDaylight_OpenFlow_Plugin:Lithium_Release_Plan