Instructions from rackspace failed with the following errors:
$ nova
ERROR: six
$ nova
ERROR: 'module' object has no attribute 'add_arg'
$ AuthSystemNotFound: 'rackspace'
$ AuthSystemNotFound: 'rackspace_uk'
With some help from @mattt and @annegentle on #rackspace on Freenode, I got it working with this:
$ pip install rackspace-auth-openstack==1.0 rackspace-novaclient==1.3 python-novaclient==2.13.0