hooks: Support OVS in OpenStack Network vNIC hook

The hook will now support connecting a vNIC both to a standard linux
bridge, and an OVS bridge.

The hook should work in tandem with the corresponding OpenStack Network
plugin: Linux Bridge or OVS plugin.

Change-Id: Ieded0281b8c5b89ad9380881a93d408e09624f38
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/15410
Reviewed-by: Dan Kenigsberg <danken@redhat.com>