Added support to use docker with Rackspace Cloud Servers

This adds a few modifications to puppet and the Vagrantfile to spin up docker in Rackspace Cloud Servers.  Cloud Servers images don't have puppet by default, so I also added a line to automatically install that before running puppet so that should be useful if using any other type of image that doesn't have puppet built in.  

I also made a tweak to the group to set it to vagrant instead of ubuntu and set /home/vagrant to ensure as a directory instead of a file.

Tested with Vagrant v1.1.2.