Fix bug with time_based run

We need to clear the FIO_FILE_DONE flag and the number of
files done, to avoid do_io() exiting quickly for a re-run.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.c b/fio.c
index 6483e64..9e93159 100644
--- a/fio.c
+++ b/fio.c
@@ -736,11 +736,14 @@
 
 	td->last_was_sync = 0;
 
+	td->nr_done_files = 0;
+
 	for_each_file(td, f, i)
 		td_io_close_file(td, f);
 
 	ret = 0;
 	for_each_file(td, f, i) {
+		f->flags &= ~FIO_FILE_DONE;
 		ret = td_io_open_file(td, f);
 		if (ret)
 			break;