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`.)
@singingwolfboy (I also just added this as a comment in @nedbat 's google doc). I believe that we need an aspen release branch on the configuration repo also. That way we can verify vagrant/base/devstack and /fullstack Vagrantfiles, then create the vagrant images for those and upload to s3, and update the Vagrantfiles in vagrant/release with the new .vbox names.
Also if we later find that we need to apply hotfixes to the configuration repo we will need to do that on the aspen release branch, in order to avoid pulling in more (possibly breaking) changes that might have gotten merged to master in the configuration repo in the interim.