migrate paho.mqtt CallbackAPIVersion to VERSION2 (#225)

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

@@ -0,0 +1,14 @@
+from weakref import WeakValueDictionary
+
+
+class Singleton(type):
+    _instances = WeakValueDictionary()
+
+    def __call__(cls, *args, **kwargs):
+        # logger_mqtt.debug('singleton: __call__')
+        if cls not in cls._instances:
+            instance = super(Singleton,
+                             cls).__call__(*args, **kwargs)
+            cls._instances[cls] = instance
+
+        return cls._instances[cls]