Exit with error on signal

Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
diff --git a/fio.c b/fio.c
index a737a31..284e9f2 100644
--- a/fio.c
+++ b/fio.c
@@ -126,6 +126,7 @@
 	if (threads) {
 		log_info("\nfio: terminating on signal %d\n", sig);
 		fflush(stdout);
+		exit_value = 128;
 		terminate_threads(TERMINATE_ALL);
 	}
 }