Added Vagrantfile for testing provisions.

Run "vagrant up" to create the defined VMs in the Vagrantfile and to provision the ```memcached.yml``` playbook, which imports this role.
 
 At the moment, there are defined the following boxes:
 
 * ```debian-720```: Debian 7.2.0 from Chef's Bento project.
 * ```ubuntu-1204```: Ubuntu 12.04 from Chef's Bento project.
 
 More boxes can be added by adding a new entry in the ```boxes``` array in the Vagrantfile. No other change should be necessary.