PWMProbes: Fix Singleton to attach it to the specific cls

Previously, the hasattr call would use MRO to find _instance on the
parent so if the parent were instantiated before the child, the child
would reuse the parent's instance.

IBM#38
Signed-off-by: Gabe Goodhart <ghart@us.ibm.com>

oper8/watch_manager/python_watch_manager/utils/types.py

@@ -263,7 +263,9 @@ def __call__(cls, *args, **kwargs):
         if getattr(cls, "_disable_singleton", False):
             return type.__call__(cls, *args, **kwargs)
 
-        if not hasattr(cls, "_instance"):
+        # The _instance is attached to the class itself without looking upwards
+        # into any parent classes
+        if "_instance" not in cls.__dict__:
             cls._instance = type.__call__(cls, *args, **kwargs)
         return cls._instance