Bz1129462 openstack handle metering

Fix a bug where the Metering Service (Ceilometer) was not appropriately wrapped in the new Openstack Service Delegate construct introduced for Tenant support in ManageIQ.

This also introduces the ability for new Openstack services to be supported without requiring a service wrapper.

https://bugzilla.redhat.com/show_bug.cgi?id=1129462
Is ceilometer an optional service? If so, it may be clearer if you put an explicit nil entry for it in the SERVICE_FALL_BACK hash.