subnetpool address scope change event should include the old address scope id

[Steve Ruan]

in neutron.db.db_base_plugin_v2,
def update_subnetpool(self, context, id, subnetpool):
....
            if address_scope_changed:
            # Notify about the update of subnetpool's address scope
            kwargs = {'context': context, 'subnetpool_id': id}
            registry.notify(resources.SUBNETPOOL_ADDRESS_SCOPE,
                            events.AFTER_UPDATE,
                            self.update_subnetpool,
                            **kwargs)

This kwargs ONLY includes subnetpool_id, in some cases, we want to know the subnetpool old address scope id.

Here is the use case,
To develop bgp vpn in neutron-dynamic-routing, each bgpvpn is associated to address scope, bgpvpn routes only include the subnets of same address scope.
If the subnetpool change its address scope, for some bgpvpnvs associated to old address scope, it should delete the routes; for some bgpvpns associated to new address scope, it should add new routes.

If this event does not include old address_scope_id, bgpvpn can not delete old routes.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/337662

[OpenStack Infra (hudson-openstack)]

Change abandoned by Armando Migliaccio (<email address hidden>) on branch: master
Review: https://review.openstack.org/337662
Reason: This review is > 4 weeks without comment, and failed Jenkins the last time it was checked. We are abandoning this for now. Feel free to reactivate the review by pressing the restore button and leaving a 'recheck' comment to get fresh test results.