test/zdtm.sh: sanity check for crtools existence

Otherwise test goes too far.
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrey Vagin <avagin@gmail.com>

test/zdtm.sh

@@ -42,6 +42,7 @@ static/shm
 "
 
 CRTOOLS=`pwd`/`dirname $0`/../crtools
+test -x $CRTOOLS || exit 1
 
 run_test()
 {