CACHE_REQ: Make cache_req_{create_and_,}add_result() more generic
    
    This patch is preparing the field for coming up patches where this
    function will be re-used. In order to do so, let's remove the dependency
    for tevent states on both cache_req_create_and_add_result() and
    cache_req_add_result().
    
    Related:
    https://pagure.io/sssd/sssd/issue/3001
    
    Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>