first cut at Rackspace upload functionality

Rackspace uses a task-based upload scheme that, as of the time of this patch,
is not part of upstream OpenStack.  To use it we have to make use of the
pyrax Python binding.

The "provider" in the case of Rackspace is expected to be one of the standard
rackspace region codes.  Known regions supported right now are:

ORD, DFW and SYD

On the Factory CLI these should be specified as @ORD, etc.
add missing vhd source
update Rackspace RPM requires to include python-pyrax
Merge pull request #344 from redhat-imaging/feature/rackspace_upload_pyrax2

Feature/rackspace upload pyrax2