Fix vips validation for subnet deletion
Fix vips validation for subnet deletion

Change-Id: Id0edf3760c55d198d7ce2cd824f713b297e7bbc9
Depends-On: I7c88b4ced51050ebb26eb0170d0e20f3e6c5a024
Closes-Bug: OPENSTACK-2718

nuagenetworks/nuage-openstack-neutron,nuagenetworks/nuage-openstack-neutron