Update the Locate payloads

This change updates the Locate payloads to the current payload
format, adding properties for different payload attributes and
adding comparison and string operators. Changes are also made to
the PyKMIP clients and the surrounding testing infrastructure to
reflect the payload changes. An official unit test suite for the
Locate payloads has also been included, which will eventually
replace the existing Locate message tests elsewhere in the test
suite.

This change prepares the Locate payloads for future updates to
support KMIP 2.0.

kmip/services/server/engine.py

@@ -1563,9 +1563,9 @@ class KmipEngine(object):
 
             managed_objects = managed_objects_filtered
 
-        unique_identifiers = [attributes.UniqueIdentifier(
-                            str(managed_object.unique_identifier))
-                            for managed_object in managed_objects]
+        unique_identifiers = [
+            str(x.unique_identifier) for x in managed_objects
+        ]
 
         response_payload = payloads.LocateResponsePayload(
             unique_identifiers=unique_identifiers