Write script to clean up old versions on Vagrant Cloud

[ksclarke]

Probably not a high priority, but would be nice to have a script to clean up nightly snapshots of packer-samvera that are persisted to Vagrant Cloud. Doing snapshots nightly produces a lot of boxes. There isn't an explicit storage limit with Vagrant Cloud but I'd bet there is an unofficial one, at which point they ping people and ask about their disk usage.