Add Fedora 19 to the nodepool (devstack-f19-check)

HP doesn't yet seem to have a compatible Fedora 19 base image so
this currently only configures the Rackspace providers to use
Fedora 19. Given that we use RAX for check tests anyway
(and that is where we'll start Fedora) this seems like
a good first step.

Change-Id: I599f7fd5e25d25f79eabbbc0b7e7b1b60c4c3a2a
Merge "Add Fedora 19 to the nodepool (devstack-f19-check)"