BZ #1151606: Do not destroy VIPs when assigning interfaces

https://bugzilla.redhat.com/show_bug.cgi?id=1151606

When interfaces are being assigned to subnets, Staypuft was destroying
the VIPs. And they would not get re-created. This keeps them from being
destroyed when a subnet with VIPs is moved around.
Merge pull request #360 from bcrochet/bz/1151606

BZ #1151606: Do not destroy VIPs when assigning interfaces