Improve random verify block sorting

Add an option to control it and also check the nosort flag in file
layout to further catch a case where sorting isn't needed.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index ec08e42..ddc7e23 100644
--- a/fio.h
+++ b/fio.h
@@ -238,6 +238,7 @@
 	FIO_FILE_UNLINK		= 1 << 1,	/* unlink on close */
 	FIO_FILE_CLOSING	= 1 << 2,	/* file being closed */
 	FIO_FILE_EXISTS		= 1 << 3,	/* no need to create */
+	FIO_FILE_NOSORT		= 1 << 4,	/* don't sort verify blocks */
 };
 
 /*
@@ -356,6 +357,7 @@
 	unsigned int end_fsync;
 	unsigned int sync_io;
 	unsigned int verify;
+	unsigned int verifysort;
 	unsigned int use_thread;
 	unsigned int unlink;
 	unsigned int do_disk_util;