Add verify_fatal option

Causes fio to exit after a single block verification failure, instead of
checking the remainder as well.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index 0373d2a..6b11155 100644
--- a/fio.h
+++ b/fio.h
@@ -423,6 +423,7 @@
 	unsigned int verify_offset;
 	unsigned int verify_pattern;
 	unsigned int verify_pattern_bytes;
+	unsigned int verify_fatal;
 	unsigned int use_thread;
 	unsigned int unlink;
 	unsigned int do_disk_util;