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/pie/sqltypes.py

@@ -107,7 +107,10 @@ class EnumType(types.TypeDecorator):
             value(Enum): An Enum instance whose integer value is to be stored.
             dialect(string): SQL dialect
         """
-        return value.value
+        if value:
+            return value.value
+        else:
+            return -1
 
     def process_result_value(self, value, dialect):
         """
@@ -120,6 +123,8 @@ class EnumType(types.TypeDecorator):
                 to create the Enum
             dialect(string): SQL dialect
         """
+        if value == -1:
+            return None
         return self._cls(value)