Add multiple-driver support to the notifier api.
Add multiple-driver support to the notifier api.

Move all of the functionality previously provided by the list_notifier
into the basic notifier api.  Move and restructure tests accordingly.

Remove the list_notifier file and test file.

For bug 1025820

Change-Id: Idf7cb975dd78e9951188781622a4d10ca466b154

WiFast/pbr,openstack-dev/pbr,klmitch/pbr,JioCloud/pbr,klmitch/pbr,citrix-openstack-build/pbr,openstack-dev/pbr,citrix-openstack-build/pbr,WiFast/pbr,varunarya10/pbr,emonty/oslo-packaging,citrix-openstack-build/pbr,varunarya10/pbr,JioCloud/pbr,redhat-openstack/pbr,openstack-dev/pbr,redhat-openstack/pbr,emonty/oslo-packaging