Add usage command to show usage for single tenant

The usage-list command is admin-only so add a usage command so
that users can see their usage like they do in horizon. Only
admins can see usage for other tenants, so default the value of
tenant to the tenant_id of the current credentials.

Change-Id: Icd6fec36f1f4145b92b227031e5df23db11737f0
Merge "Add usage command to show usage for single tenant"