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__

Also remove class SubStringMatcher becasue this class isn't used
following commit 7035639dfd239b52d4ed46aae50f78d16ec8cbfe.

Change-Id: Ia2131f72a79226b0c2f3662b84661eb870d1d692

swift/common/manager.py

@@ -441,6 +441,9 @@ class Server(object):
         except AttributeError:
             return False
 
+    def __ne__(self, other):
+        return not self.__eq__(other)
+
     def get_pid_file_name(self, conf_file):
         """Translate conf_file to a corresponding pid_file
 

test/unit/common/ring/test_builder.py

@@ -2154,13 +2154,6 @@ class TestRingBuilder(unittest.TestCase):
         # now double up a device assignment
         rb._replica2part2dev[1][200] = rb._replica2part2dev[2][200]
 
-        class SubStringMatcher(object):
-            def __init__(self, substr):
-                self.substr = substr
-
-            def __eq__(self, other):
-                return self.substr in other
-
         with self.assertRaises(exceptions.RingValidationError) as e:
             rb.validate()