rbd: clearly mark open function as deprecated
Use the notation described in the new API stability doc.
@@ -327,7 +327,7 @@ func (image *Image) Rename(destname string) error {
return err
}
-// Open the rbd image.
+// Open the rbd image (DEPRECATED).
//
// Deprecated: The Open function was provided in earlier versions of the API
// and now exists to support older code. The use of OpenImage and
