external driver support

[jason-neumann]

I was trying to use the kubevirt driver with this and found that when i set the driver name to kubevirt for a scenario and run molecule list i get an error that says "kubevirt is not one of <list_of_strings>". I found that list inside src/molecule/data/molecule.json got added as part of #3668. I tried some of the other drivers in the ansible-community project and they do the same. Are you expecting these other drivers to modify the molecule.json file when they are installed to include themselves in the schema or do you plan on changing the schema to allow the driver name to be any string?

[zhan9san]

@jason-neumann would you minding creating a PR to fix it?

[jason-neumann]

I found #3689 has a good bit of conversation on this. I've rolled back to 4.0.1 currently and don't have the cycles to implement a fix. If we decide to use what I put together and the currently open issue hasn't been resolved in a couple of weeks I might find some cycles for it.