- cosmetic changes in mdapi DLD

- more fixes in GNS stuff:
  - fixes with refcount onto @dchild in ll_gns_mount_object() for error control paths
  - fixing using accessing @dchild in the case of IS_ERR(dchild)

  - disabled checking for GNS file in mds_open(), thus GNS mount points are also
    opening by now. This is needed, because in taking lock we can't reliable to detect
    GNS objects on MDS. Checking just suid bit and skip open such a dirs is not correct
    as one may create structure like dir/dir/dir and mark all of them by suid.

  - cleanups in sanity-gns.sh. Added few new tests for odd conditions like mount object
    is symlink, dir, etc. Added test for changing mount object name to "." and "..".
    Grouping tests into 2 groups:

    (1) general GNS tests - mounting/umounting on timeout with different conditions
    with possible deadlocks, races, etc.

    (2) checking for odd conditions like recursive suid bit marked mount points, etc