Add MeteringDeletate to Openstack Handle

Adds the ability to connect to Ceilometer through the openstack delegate.

https://bugzilla.redhat.com/show_bug.cgi?id=1129462
Allow non-wrapped openstack services

As Openstack evolves, there are likely to be new services we need to support.
This change will allow us to return the underlying Fog-based Openstack service
if we haven't yet wrapped Openstack service with a corresponding
tenant-supported Openstack Service Delegate class.

I'm a little torn on this commit, because the presence of a new Openstack
service should give us pause and require that we think about whether the service
needs to be restricted to tenant-based operations.

However, I also know how much the Openstack ecosystem changes and evolves.  So,
it makes sense to be able to simply pass through to the underlying service until
we absolutely need to wrap the service with tenant-based operations.

Associated with:
https://bugzilla.redhat.com/show_bug.cgi?id=1129462
Exclude Ceilometer from service fallback list

Be explicit in the fact that there is no service fallback for the Openstack
Ceilometer service.
Merge pull request #385 from blomquisg/bz1129462-openstack-handle-metering

Bz1129462 openstack handle metering