Not seeing attach detach instance interfaces

As part of https://bugs.launchpad.net/searchlight/+bug/1565028 i requested proper notifications for interface attach/detach within nova; before we relied on port.update events and determining whether or not the event referred to an attach/detach event and then for detach code to find which instance a port was attached to. If we don't get the proper notification we'll need to make a call on how to handle it. I'm strongly opposed to having to deal with things on a very specific basis because it sets us up for getting out of sync with the services, increases testing etc but we may not have much choice in some cases.