Fix bad sscan() -> scanf() conversion

Caused fio to stall waiting for disk updates.

Also add --debug=diskutil debug option, to trace what diskutil is doing.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/debug.h b/debug.h
index b11a901..22577a8 100644
--- a/debug.h
+++ b/debug.h
@@ -13,6 +13,7 @@
 	FD_VERIFY,
 	FD_RANDOM,
 	FD_PARSE,
+	FD_DISKUTIL,
 	FD_DEBUG_MAX,
 };