CACHE_REQ: Make use of cache_req_ncache_filter_fn()
    
    This patch makes use of cache_req_ncache_filter_fn() in order to process
    the result of a cache_req search and then filter out all the results
    that are present in the negative cache.
    
    The "post cache_req search" result processing is done basically in two
    different cases:
    - plugins which don't use name as an input token (group_by_id, user_by_id
      and object_by_id), but still can be affected by filter_{users,groups}
      options;
    - plugins responsible for groups and users enumeration (enum_groups and
      enum_users);
    
    Resolves:
    https://pagure.io/SSSD/sssd/issue/3362
    
    Signed-off-by: Fabiano Fidêncio <fidencio@redhat.com>
    
    Reviewed-by: Pavel Březina <pbrezina@redhat.com>