Fix pkt_in exception when host is not found

Change-Id: I233bb8d255d5849a7f646e4c76bbba2de9ee40e8

Fix SwitchDiscoveryManager trying to delete OpenFlow port (OVX-431)

Change-Id: I0cf00f21d4e83767abca15edd157997bf5f9f90f

Remove all links invovled in switch removal

Change-Id: I17e358e8eb9cf192729cb0a4f1b563ac7106ff60