cloud-config validate without cloudinit

A quick hack to let you validate your CoreOS cloud-config user_data file without having to install coreos-cloudinit (though you do need internet access):

curl 'https://validate.core-os.net/validate' -X PUT --data-binary '@user_data'

This makes use of CoreOS's online validator, but without having to copy/paste which can be a little fiddly when SSH'd somewhere.