sbus: use 'path/*' to represent a D-Bus fallback
    
    Use 'path/*' instead of 'path*' since it better describes what
    we are actually doing i.e. registering a message handler for a
    subtree.
    
    Although D-Bus fallback will invoke a message handler for both
    'path' and 'path/subtree' object paths it does not make usually
    sence to support the same interfaces for both parent and it
    children.
    
    This commit also renames related functions to better describe
    what are they doing.
    
    Note: the tilda in comments is used to suppress -Wcomment warning
    
    Preparation for:
    https://fedorahosted.org/sssd/ticket/2339
    
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>