feat(Vagrantfile) Use box versions, remove monkey patch.

As of 308 we generate json files that include version metadata for the
Vagrant boxes. Also the monkey patching has been moved into the box so
it can be removed from here.

Note: The version constraint ensures new instances will download 308 or
later but this is not enforced on existing instances. Since the monkey
patching is required just to get previous versions of CoreOS to boot
users should not update to this revision if old instances are in use.
Merge pull request #95 from marineam/master

feat(Vagrantfile) Use box versions, remove monkey patch.
Add ability to port-forward TCP docker service to host machine

Vagrantfile will check if $expose_docker_tcp is set in config.rb, and
will forwad the docker port (tcp/4243) to the specified port on the host.

Service for docker to listen on port 4243 added to user-data.
Merge pull request #100 from mattbailey/master

Add ability to port-forward TCP docker service to host machine