zdtm/vdso: Add test for restoring task without vdso blob

Check that task without vvar & vdso blobs is restored without them.

Reviewed-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Dmitry Safonov <dsafonov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>