Wire-up FlowManager to PolicyManager/EndpointManager

FlowManager now listens to end-point and end-point group
updates to generate flow-table modifications. Also removed
classes Inventory and Enforcer as they don't look
useful anymore (corresponding tests are also removed).
Converted the flowManager tests into "real" unit-tests.
Fixed a couple of issues in PolicyManager/EndpointManager:
- implemented getEndpointsForGroup
- DomainListener::objectUpdated() was deleting endpoint
  groups while iterating over them which messes up the
  iterators
Added a utility function to modb::MAC class.

Change-Id: Ibc210187c2a3bcd289fc9a28bb0abb16bf91645d
Signed-off-by: Amit Bose <bose@noironetworks.com>
Merge "Wire-up FlowManager to PolicyManager/EndpointManager"