Vagrant Provider for Integration Testing

[jGleitz]

I have made some adaptions to this repository in order to run it against Vagrant machines (via terraform-provider-vagrant). My goal is to have the setup running against Vagrant in CI so I can test updates before deploying them. I would be glad to merge my changes back to this repository.

Would you be interested in

1. a PR that adapts the terraform setup so that it can be used againts Vagrant?
2. a PR that adds the Vagrant provider so that others can use it as well?
3. a PR that adds integration tests to this repository so that changes can be checked in CI?