Take advantage of the kitchen-vagrant Vagrantfile template hook 

[kitchen-vagrant](https://github.com/test-kitchen/kitchen-vagrant) `v0.12.0` added support for providing a custom `Vagrantfile` [ERB](http://ruby-doc.org/stdlib-1.9.3/libdoc/erb/rdoc/ERB.html) template. This allows us to enable a variety of Vagrant plugins during the test-kitchen runs.