Adds simple tenant usage support for the Nova V3 API

Adds support and tests for the os-simple-tenant-usage
extension for the Nova V3 API. There are no
differences between the V2 and V3 API and this change
adds the client code to enable the usage command. Note
that with nomenclature change from tenant to project
occuring in Nova there will be a difference between
the V2 and V3 API in the future.

Differences between the V2 and V3 API are described here:
https://wiki.openstack.org/wiki/NovaAPIv2tov3

Partially implements blueprint v3-api

Change-Id: Iddf6211c9c87cbb191d9a5d5a65710b343c30e67
Merge "Adds simple tenant usage support for the Nova V3 API"