Provide a mechanism for openflowplugin to determine on which instance of the controller it should assume mastership of a switch

An openflow switch may be connected to multiple instances of the controller for HA such that when one instance of the controller was down another instance would take mastership of that switch. To be able to do so the openflowplugin requires some mechanism to determine if a switch is connected to multiple controller insstances and which instance in the controller should own (or be master) for that switch. Without this support OPNFLWPLUG-529 cannot be fixed.