NSX: Fix 404 from raising on update_port if lswitch not in nsx

If one calls update_port and the lport is not stored in the nvp_lport_mapping
table in the database and the lswitch the lport resides on is not in nsx
we should catch NotFound and return the port in error state. This patch fixes
this for havana and also corrects the fake_api_client to raise NotFound in this
case. This problem does not exist in IceHouse though as we query NSX with *
which does not raise NotFound.

Change-Id: Ia01f900ade714b512b49fd3e803159a27599fee1
Closes-bug: #1311300
Related-bug: #1311291
Merge "NSX: Fix 404 from raising on update_port if lswitch not in nsx" into stable/havana