zdtm: don't used --log-pid by default

I added this options and I found, that it was a bad idea.
Currently crtools prints PID for each message, so
--log-pid can help if an error in the restorer code.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>