zdtm: check a ghost file in a read-only directory

=[log]=> dump/zdtm/static/unlink_fstat00/39/1/restore.log
------------------------ grep Error ------------------------
(00.097701)      4: Error (files-reg.c:1231): Can't link zdtm/static/unlink_fstat00.test/test\file'
(00.097707)      4: Error (files-reg.c:1431): Can't link zdtm/static/unlink_fstat00.test/test\file'
(00.097952)      1: Error (cr-restore.c:1404): 4 exited, status=1
(00.108085) Error (cr-restore.c:1407): 64 killed by signal 9: Killed
(00.114341) Error (cr-restore.c:2246): Restoring FAILED.
------------------------ ERROR OVER ------------------------

v2: add a new test instead of changing the existing one.
Signed-off-by: Andrew Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>