Add zero_buffers option

This option will cause all IO buffers to be initialized to all zeroes.
The default is to fill them with random data.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 0893a20..9490edc 100644
--- a/fio.h
+++ b/fio.h
@@ -412,6 +412,7 @@
 	unsigned int file_service_type;
 	unsigned int group_reporting;
 	unsigned int fadvise_hint;
+	unsigned int zero_buffers;
 
 	char *read_iolog_file;
 	char *write_iolog_file;