Add __ne__ built-in function

In Python 3 __ne__ by default delegates to __eq__ and inverts the
result, but in Python 2 they urge you to define __ne__ when you
define __eq__ for it to work properly [1].There are no implied
relationships among the comparison operators. The truth of x==y
does not imply that x!=y is false. Accordingly, when defining
__eq__(), one should also define __ne__() so that the operators
will behave as expected.
[1]https://docs.python.org/2/reference/datamodel.html#object.__ne__

Change-Id: I5485022f010cdcb88c0d4ebe5c44a39a1bf242b0

tests/unit/utils.py

@@ -494,6 +494,9 @@ class CaptureOutput(object):
     def __eq__(self, other):
         return self.out == other
 
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
     def __getattr__(self, name):
         return getattr(self.out, name)