Add SetAttribute support to the server

This change adds SetAttribute operation support to the PyKMIP
server, including additional attribute policy functionality to
check for certain attribute characteristics that preclude
SetAttribute operation functionality. Specifically, the operation
cannot set the value of any multivalued attribute nor the value
of any attribute not modifiable by the client. New unit tests
have been added to cover these changes.

Partially implements #547

kmip/services/server/policy.py

@@ -1155,6 +1155,20 @@ class AttributePolicy(object):
         rule_set = self._attribute_rule_sets.get(attribute)
         return rule_set.deletable_by_client
 
+    def is_attribute_modifiable_by_client(self, attribute):
+        """
+        Check if the attribute can be modified by the client.
+
+        Args:
+            attribute (string): The name of the attribute (e.g., "Name").
+
+        Returns:
+            bool: True if the attribute can be modified by the client. False
+                otherwise.
+        """
+        rule_set = self._attribute_rule_sets.get(attribute)
+        return rule_set.modifiable_by_client
+
     def is_attribute_applicable_to_object_type(self, attribute, object_type):
         """
         Check if the attribute is supported by the given object type.