Python 3: set __bool__() method on Namespace

The Python 2 __nonzero__() method was renamed to __bool__() in Python 3.

Create a __bool__ alias to __nonzero__ in the Namespace class.

Change-Id: I2ad3b3522b9ee2d33a5eee8886ee5f07776fb449

ceilometer/transformer/__init__.py

@@ -89,3 +89,4 @@ class Namespace(object):
 
     def __nonzero__(self):
         return len(self.__dict__) > 0
+    __bool__ = __nonzero__