adding vagrant to help linux/mac test in windows

https://github.com/stefanpenner/ember-cli/issues/1558#issuecomment-51205776

I'm familiar with Vagrant so I made a script that will grab a Windows
box from vagrantcloud.com and set it up to `npm test`.

I could not test this with a Linux host because VMs inside VMs is tricky
business, but it should work.