add support for neutron/nova notifications

This adds options to configure the Neutron -> Nova notifications of port
status and data changes.  Requires a recent puppet-neutron module with
neutron::server::notifications
(https://review.openstack.org/#/c/85269/).

Change-Id: I26684a8fe5df79db6b68a5bd733619517376660c
Closes-bug: 1306337