blsuki: Error out if unexpected arguments are supplied

blsuki: Error out if unexpected arguments are supplied

This can be especially helpful, as the Fedora version of the blscfg
actually made use of positional arguments, but current implementation
switched to parameters. For example what used to be "blscfg (hd0,gpt2)/..."
now should be "blscfg --path (hd0,gpt2)/...)". In case of old configs/scripts
still supplying positional arguments we will now error out instead of just
ignoring them and falling back to defaults silently.

Signed-off-by: Radoslav Kolev <radoslav.kolev@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>