Create a SerializableComparable class

Create a SerializableComparable class derived from the Serializable
class.

Added the following functions to the SerializableComparable class:
  '__eq__'
  '__ne__'

Disable the '__hash__' function in the SerializableComparable class as
some derived classes are mutable.

Use the SerializableComparable class in hardware.py and
extensions/base.py

This should make unit testing users of the class easier when doing a
self.assertEqual() or self.assertNotEqual()

Added some initial unit testing for encoding.py

Change-Id: If0f14b3bfe7f1391f65dd730a16a534afed0da82

ironic_python_agent/encoding.py

@@ -25,6 +25,24 @@ class Serializable(object):
         return dict((f, getattr(self, f)) for f in self.serializable_fields)
 
 
+class SerializableComparable(Serializable):
+    """A Serializable class which supports some comparison operators
+
+    This class supports the '__eq__' and '__ne__' comparison operators, but
+    intentionally disables the '__hash__' operator as some child classes may be
+    mutable.  The addition of these comparison operators is mainly used to
+    assist with unit testing.
+    """
+
+    __hash__ = None
+
+    def __eq__(self, other):
+        return self.serialize() == other.serialize()
+
+    def __ne__(self, other):
+        return self.serialize() != other.serialize()
+
+
 class RESTJSONEncoder(json.JSONEncoder):
     """A slightly customized JSON encoder."""
     def encode(self, o):