idviews: Ignore host or hostgroup options set to None
    
    Since passing --hosts= or --hostsgroups= to idview-apply or unapply
    commands does not make sense, ignore it.
    
    https://fedorahosted.org/freeipa/ticket/4806
    
    Reviewed-By: Petr Vobornik <pvoborni@redhat.com>