Cisco N1kv: Remove vmnetwork delete REST call on last port delete

Remove the vm network delete call to the VSM on final port call and
ensure that vm network is deleted from the database when the port count
becomes 0.

Change-Id: I6c08a099adfce2fdba8eefec6aadeb68a780ac37
Closes-Bug: 1373547
(cherry picked from commit 4e1c4cbcd71833095534bea9ff7617c582c300d2)
Merge "Cisco N1kv: Remove vmnetwork delete REST call on last port delete" into stable/juno