Added vagrant-aspen playbook and vagrant conf

@jarv, can you review this? I'm in the process of testing, to be sure that this works the way I expect. (I mostly copied the vagrant file from `vagrant-fullstack.yml`.)
@clytwynec Please see the previous discussion in this pull request. We *will* update the release version of this file, but that requires creating a Vagrant box, which we can't do until aspen is actually released.