Vagrantfile: Add support for VMWare Fusion provider 

As a user who has blown $150 on VMWare Fusion and vagrant-vmware, I would like to use my new shiny to hack on Docker. Docker already has a multi-provider Vagrantfile, so adding another one presents little risk.

Known Issues:
- The docker install of a new kernel breaks the Vagrant shared folder.
 - This seems to be because the VMWare hgfs module doesn't build against a 3.8 kernel.
 - I don't believe that the shared folder support is actually in use