Add payload base classes to prepare for simplifying the client

This change adds payload request and response base classes to
prepare for future simplification updates to the current client
architecture. No new tests are required for this change.

kmip/core/messages/payloads/get_attributes.py

@@ -17,9 +17,10 @@ from kmip.core import exceptions
 from kmip.core import objects
 from kmip.core import primitives
 from kmip.core import utils
+from kmip.core.messages.payloads import base
 
 
-class GetAttributesRequestPayload(primitives.Struct):
+class GetAttributesRequestPayload(base.RequestPayload):
     """
     A request payload for the GetAttributes operation.
 
@@ -48,8 +49,7 @@ class GetAttributesRequestPayload(primitives.Struct):
                 attributes associated with the managed object. Optional,
                 defaults to None.
         """
-        super(GetAttributesRequestPayload, self).__init__(
-            enums.Tags.REQUEST_PAYLOAD)
+        super(GetAttributesRequestPayload, self).__init__()
 
         self._unique_identifier = None
         self._attribute_names = list()
@@ -272,7 +272,7 @@ class GetAttributesRequestPayload(primitives.Struct):
             return NotImplemented
 
 
-class GetAttributesResponsePayload(primitives.Struct):
+class GetAttributesResponsePayload(base.ResponsePayload):
     """
     A response payload for the GetAttributes operation.
 
@@ -297,8 +297,7 @@ class GetAttributesResponsePayload(primitives.Struct):
             attributes (list): A list of attribute structures associated with
                 the managed object. Optional, defaults to None.
         """
-        super(GetAttributesResponsePayload, self).__init__(
-            enums.Tags.RESPONSE_PAYLOAD)
+        super(GetAttributesResponsePayload, self).__init__()
 
         self._unique_identifier = None
         self._attributes = list()