Updates Vagrant to use Berkshelf

This switches the Vagrantfile to use berkshelf for the supermarket
cookbook so we can develop the two independently.
Updates README to reflect the berks plugin use

README now notes that you need to install the vagrant-berkshelf plugin
to run vagrant.
Removes cookbook from the repo

This does the actual work of removing the cookbook that is no longer
needed.
Cleans up testing code
Merge pull request #387 from opscode/cwebberOps/seperate-cookbook

Remove the supermarket cookbook from the codebase