fix(image_to_vm): Use vmdk disks for vagrant and write configs.

Vagrant will need the virtualbox ovf plus its own Vagrantfile config.
After this we will need an optional "package" step to this script to
take these files and bundle them into a .box tarball. This could also be
used to switch from .ovf+vmdk for plain virtualbox images to a bundled
.ova archive which combines the two.