The reason nobody moved on this is because it just doesn't make sense to introduce vagrant boxes to test single extensions or libraries, however elegant it may look in isolation.

Since this targets an unsupported branch of PHP, and since I don't think anyone could merge a PR targeting a supported branch anyway, I'm closing this PR.

It may be the case that we could make use of a vagrant box during testing, but it would have to serve a wider purpose than to test one library or extension.