Fix resource mapping for Rackspace

resource_mapping() always returns all existing resource names and
their classes. available_resource_mapping() takes the dependencies
into account and only returns the ones whose dependencies have been
met.

Partial-Bug: #1271226
Change-Id: I3a7467e87f7ff81badd51f121ecea98f2924e506
Merge "Fix resource mapping for Rackspace"