Duplicated the shell provisioner; there's one shell provisioner for VMWare and another for VirtualBox; made each only apply to their respective hypervisor with 'only' parameters; removed the call to the VirtualBox script in the VMWare provisioner and vice versa.
Merge branch 'master' of github.com:nickchappell/packer-templates
Made the output-virtualbox folder ignore a little more general.