First cut at the notifier API

See:

  https://wiki.openstack.org/wiki/Oslo/Messaging#Emitting_Notifications

Change-Id: Icbc16c8b089158e398acebaac3c599fe529981b7
Co-authored-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Add some test code

Right so ... it seems this stuff basically works!

Change-Id: I3c575ae9364e280e7523bc3856e5d6f1948826ad