Add optional parameters 'limit' and 'marker' to the
os-simple-tenant-usage endpoints for pagaination.
/os-simple-tenant-usage?limit={limit}&marker={instance_uuid}
/os-simple-tenant-usage/{tenant}?limit={limit}&marker={instance_uuid}
The aggregate usage totals may no longer reflect all instances for a
tenant, but rather just the instances for a given page. API consumers
will need to stitch the aggregate data back together (add the totals)
if a tenant's instances span several pages.
Implements blueprint paginate-simple-tenant-usage
Change-Id: Ic8e9f869f1b855f968967bedbf77542f287f26c0