client: fix hiding of commands which lack server support
    
    Rather than checking the server counterpart's NO_CLI, which may be False
    even for commands supported on the server, check wheter the server
    counterpart is a command defined on the server or a local placeholder.
    
    https://fedorahosted.org/freeipa/ticket/6089
    
    Reviewed-By: Florence Blanc-Renaud <flo@redhat.com>