Seperate template to create Vagrant box

This separates creation of VMware images and Vagrant boxes.

Since `vagrant` is a post-processor in Packer, we can't specify any scripts that will only apply to to `virtualbox` builder -> `vagrant` post-processor pipeline. (There may be a way to do this I'm not aware of, but I don't think having everything in the same template buys us anything.)

We need to do this because it's not possible to specify `vagrant` as the `ssh_username` - it must be `ubuntu` (a login timeout is the result if Packer can't log into the VM on creation).

The Vagrant user set script is referenced only in the relevant template.