Update the object data model to support storing key wrapping data

This change updates the KMIP object model to support explicitly
storing key wrapping data attributes. Key wrapping data is treated
externally as a dictionary and is stored as individual fields in
the back end. Various unit tests have been updated and added to
support these additions.

kmip/tests/unit/pie/objects/test_key.py

@@ -94,3 +94,17 @@ class TestKey(TestCase):
         """
         dummy = DummyKey()
         self.assertFalse(dummy != dummy)
+
+    def test_key_wrapping_data_invalid(self):
+        """
+        Test that the right error is raised when setting the key wrapping
+        data with an invalid value.
+        """
+        dummy = DummyKey()
+        args = (dummy, 'key_wrapping_data', 'invalid')
+        self.assertRaisesRegexp(
+            TypeError,
+            "Key wrapping data must be a dictionary.",
+            setattr,
+            *args
+        )