Rename rackspace-nova rackspace-dfw.

Change-Id: I79d9dcdd85c39d18200ada74817a9be7431e6109
Reviewed-on: https://review.openstack.org/19552
Approved: James E. Blair <corvus@inaugust.com>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Tested-by: Jenkins