Fix adding users with correct primary and secondary groups

[ktsakalozos]

No description provided.

[johnsca]

I didn't realize when i acquiesced to Stuart's suggested param name change that it would still leave us with a mismatch between our fork and upstream, which was the whole point of getting that change upstream.

Unfortunately, that means that this change will break all of the current production charms. We'll need to either update our fork to match the param names, or provide values for all of the params and only use positional args to get around the difference in param name.