Enforce server support for DeriveKey truncation

This change updates DeriveKey support in the software server to
enforce key truncation. If the derived key is longer than the
requested cryptographic length, the derived key is truncated to
fit the requested length. A unit test has been added to cover
this update.

kmip/services/server/engine.py

@@ -1473,6 +1473,8 @@ class KmipEngine(object):
                 "The specified length exceeds the output of the derivation "
                 "method."
             )
+        if len(derived_data) > derivation_length:
+            derived_data = derived_data[:derivation_length]
 
         if payload.object_type == enums.ObjectType.SYMMETRIC_KEY:
             managed_object = objects.SymmetricKey(