Support multi-node testing in beaker workflow

[alexjfisher]

Modules such openvpn and spiped currently can't be modulesynced to use the shared actions as they require beaker setfiles with more than one host. eg https://github.com/voxpupuli/puppet-openvpn/blob/7ce40c3baa99b77880f8b5a9062bd36cc5557ad0/.github/workflows/ci.yml#L69-L85

I think the first step will be to decide what a new command line option to metadata2gha would look like and then implement that change over in https://github.com/voxpupuli/puppet_metadata

eg. maybe something like the following
--multi-node-roles server,ma:client,a

would produce setfile values of the form
ubuntu1804-64server.ma{hostname=server}-ubuntu1804-64client.a{hostname=client}

I'm setting the hostname and the 'arbitrary-role' to be the same thing. Maybe that's too limited, but maybe if it's ok for 90% of the use-cases, then that's ok. Dunno.

[ekohl]

#46 is an effort that @jhoblitt already started that looks a lot like what you're suggesting.

[jhoblitt]

#46 is waiting on review.