zdtm: wait a test process instead of output file

zdtm.sh reports error immediatly, if a test process exited or crashed.

We should be fear, that pid can be reused. There are many place, which
will fail in this case. And a chance to get this situation is really small.
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

test/zdtm.sh

@@ -426,10 +426,14 @@ EOF
 	done
 
 	echo Check results $PID
-	stop_test $tdir $tname
+	stop_test $tdir $tname || {
+		echo "Unable to stop $tname ($PID)"
+		return 2
+	}
+
 	sltime=1
 	for i in `seq 50`; do
-		test -f $test.out && break
+		kill -0 $PID > /dev/null 2>&1 || break;
 		echo Waiting...
 		sleep 0.$sltime
 		[ $sltime -lt 9 ] && sltime=$((sltime+1))