hook: noipspoof: consume libvirt's clean-traffic filter

This hook converts all vnic filters of a VM to the clean-traffic filter.
The list of valid IP addresses is specified as a VM-wide custom
property.

A VM-wide custom property has been chosen since Engine does not allow
setting per-VM vnic properties (but rather only vnic-type ones).

Change-Id: Id99d9211576235be0374bde5aea5ecf7a146b979
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/29093
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>