* Support interface addition without vlan tag in vcenter
* Support interface addition without vlan tag in vcenter

In case of vcenter mode agent always expected vlan tag and parent
interface, in case of netns both wouldnt be present. Handle
such scenario.

Change-Id: Ide5d19d01fa297d43a03db4339e4a8eb69c634c4
Closes-bug: #1745975

rombie/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller,eonpatapon/contrail-controller