hooks: Support OpenStack Network in hot plug NIC

Adding hook support for hot plugging a vNIC to the VM.
The hook should behave exactly as the before_device_create hook, so
reusing the same hook code for hot plugging.

Change-Id: I8cae1c46c6165819bc2412183a32f6b335af1811
Signed-off-by: Mike Kolesnik <mkolesni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/15988
Reviewed-by: Dan Kenigsberg <danken@redhat.com>