Have openflow switch report all flow removals

Have openflow switch report all flow removals

- Current Flow Programmer Service code in protocol_plugins.openflow
  instructs the switch to report the flow removal event to the controller
  only for hard or idle timeout flows, during flowmod message creation.
  Nevrekar pointed out in some switches a removal of openflow flows may
  be done by other entities. So in order for the app on top of controller
  to get to know about this flow deletions, we are here enabling the flow
  removal event report from the switch for all controller installed flows.

Change-Id: Iae2f7716b592269fd09c4e2fa4a18ae274367f9d
Signed-off-by: Alessandro Boch <aboch@cisco.com>