cli: abort on extra arguments

Instead of straight-out rejecting extra parameters for various nmcli sub-commands (such as "nmcli dev status", "nmcli dev wifi rescan" or "nmcli dev wifi connect", etc.), we just print a warning and go ahead.

This is unhelpful. In case the user makes a typo, we'll do the wrong thing and possibly even drown the warning in the output.

While at that, let's make the error message consistent. One less string to tranalate.