Fix overwrite for kubernetes images

Now uses overrides.yml instead of overwrite.yml

Change-Id: Ia16e8f1cb3c70261599dc4cf3fcce893442d8f24
diff --git a/classes/cluster/overrides.yml b/classes/cluster/overrides.yml
index e69de29..0b36fca 100644
--- a/classes/cluster/overrides.yml
+++ b/classes/cluster/overrides.yml
@@ -0,0 +1,2 @@
+# this file is used for dynamic metadata
+# `salt-call reclass.cluster_meta_set foo bar` can be used