Account for differences in Rackspace Cloud Glance

The Rackspace Cloud service catalog has a tenant-scoped URL
for the image service so our client implementation needs to
munge the URL a little to make it work.

Change-Id: Ic5b3702aec8c4ab373dbcf6eb8e6f164d9fd48d0
Merge "Account for differences in Rackspace Cloud Glance"