zdtm: Add sleep() to zombie00

When creating zombies we must wait for them to appear to test that we do
support zombies, but not some transient state. But the thing is that we
cannot use wait() or any other synchronous call here, thus we have to
suck and use sleep(1) :(

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>