NNI port is not removed from ONOS on OLT delete

When a request to delete OLT is performed currently the NNI port is not removed from ONOS before ofagent disconnection, this goes against the controlled disconnect behaviour outlined for OLT delete scenario and prevents ONOS from properly purging flows. Thus Flows are in PENDING_REMOVE state and the subscribers are not properly remove for ONOS.

The rw-core needs to introduce a delete of all logical ports in the UNKNOWN to DELTE parent transition.