Update close file handler to return potential error

Filesystems like NFS do return errors on close(), up until now we
have been ignoring them. Fix that. Adjust io_ops engine version
to 9, since this is an API change.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/ioengines.c b/ioengines.c
index 979ac28..a81c7b8 100644
--- a/ioengines.c
+++ b/ioengines.c
@@ -344,7 +344,7 @@
 	return 1;
 }
 
-void td_io_close_file(struct thread_data *td, struct fio_file *f)
+int td_io_close_file(struct thread_data *td, struct fio_file *f)
 {
 	if (!(f->flags & FIO_FILE_CLOSING))
 		log_file(td, f, FIO_LOG_CLOSE_FILE);
@@ -354,5 +354,5 @@
 	 */
 	f->flags |= FIO_FILE_CLOSING;
 
-	put_file(td, f);
+	return put_file(td, f);
 }