Add metering-api endpoint registration

Add calls to identity_registration to support the Ceilometer metering
service. Ideally this does not live here long-term, in favor of the
metering cookbook, but until that cookbook is ready, this is being
placed here as a stop-gap measure.

Tests added for these new endpoints. Tests pass.

Change-Id: I13cfdc0fb2f280837fb4bc06dd0e6d46f059081a
Merge "Add metering-api endpoint registration"