/cc @sethvargo - Some weirdness here but overall should work fine. I'm
not sure if there was a GH issue this should be attached to or close. To
explain:
We just use the first machine with the default provider. A
Vagrant::Environment guarantees there is at least one machine, so
`env.machine_names.first` will always work. And we can just use the
default provider because we don't really care. Finally, it can be any
old machine we pass in because we just want the "global" config to
validate and there is no way to say "don't validate machine-specific
configs", so we might as well just pick the first machine to validate.
5903bfb3c6