migrate paho.mqtt CallbackAPIVersion to VERSION2 (#225)

ha_addons/ha_addon/rootfs/home/proxy/iter_registry.py

@@ -0,0 +1,9 @@
+from abc import ABCMeta
+
+
+class AbstractIterMeta(ABCMeta):
+    def __iter__(cls):
+        for ref in cls._registry:
+            obj = ref()
+            if obj is not None:
+                yield obj