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.py

@@ -20,11 +20,11 @@ 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 GetRequestPayload(primitives.Struct):
+class GetRequestPayload(base.RequestPayload):
     """
     A request payload for the Get operation.
 
@@ -62,9 +62,7 @@ class GetRequestPayload(primitives.Struct):
                 information for wrapping the returned object. Optional,
                 defaults to None.
         """
-        super(GetRequestPayload, self).__init__(
-            enums.Tags.REQUEST_PAYLOAD
-        )
+        super(GetRequestPayload, self).__init__()
 
         self._unique_identifier = None
         self._key_format_type = None
@@ -301,7 +299,7 @@ class GetRequestPayload(primitives.Struct):
         })
 
 
-class GetResponsePayload(primitives.Struct):
+class GetResponsePayload(base.ResponsePayload):
     """
     A response payload for the Get operation.
 
@@ -330,9 +328,8 @@ class GetResponsePayload(primitives.Struct):
 
                 Optional, defaults to None. Required for read/write.
         """
-        super(GetResponsePayload, self).__init__(
-            tag=enums.Tags.RESPONSE_PAYLOAD
-        )
+        super(GetResponsePayload, self).__init__()
+
         self._object_type = None
         self._unique_identifier = None
         self._secret = None