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: I4ba5b370e34cd64b13d87ef3ce2869d224dd0969

ceilometerclient/apiclient/fake_client.py

@@ -87,6 +87,9 @@ class TestResponse(requests.Response):
                 self.headers == other.headers and
                 self._content == other._content)
 
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
 
 class FakeHTTPClient(client.HTTPClient):