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/register.py

@@ -21,11 +21,11 @@ from kmip.core import objects
 from kmip.core import primitives
 from kmip.core import secrets
 from kmip.core import utils
-
 from kmip.core.factories import secrets as secret_factory
+from kmip.core.messages.payloads import base
 
 
-class RegisterRequestPayload(primitives.Struct):
+class RegisterRequestPayload(base.RequestPayload):
     """
     A request payload for the Register operation.
 
@@ -69,9 +69,7 @@ class RegisterRequestPayload(primitives.Struct):
                 object. Added in KMIP 2.0. Optional, defaults to None.
         """
 
-        super(RegisterRequestPayload, self).__init__(
-            enums.Tags.REQUEST_PAYLOAD
-        )
+        super(RegisterRequestPayload, self).__init__()
 
         self.secret_factory = secret_factory.SecretFactory()
 
@@ -388,7 +386,7 @@ class RegisterRequestPayload(primitives.Struct):
         return '{' + value + '}'
 
 
-class RegisterResponsePayload(primitives.Struct):
+class RegisterResponsePayload(base.ResponsePayload):
     """
     A response payload for the Register operation.
 
@@ -411,9 +409,7 @@ class RegisterResponsePayload(primitives.Struct):
                 structure containing a set of attributes that were set on the
                 new object. Optional, defaults to None.
         """
-        super(RegisterResponsePayload, self).__init__(
-            enums.Tags.RESPONSE_PAYLOAD
-        )
+        super(RegisterResponsePayload, self).__init__()
 
         self._unique_identifier = None
         self._template_attribute = None