Add offset and maximum item filtering for the Locate operation

This change updates Locate operation support in the PyKMIP server,
allowing users to filter objects using the offset and maximum item
constraints. The offset constraint tells the server how many
matching items should be skipped before results are returned. The
maximum items constraint tells the server how many matching items
should be returned. Unit tests and integration tests have been
added to test and verify the correctness of this feature.

Additionally, the Locate demo scripts have also been updated to
support offset and maximum item filtering. Simply use the
"--offset-items" and "--maximum-items" flags to specify offset and
maximum item values for the Locate script to filter on.

Fixes #562

kmip/demos/utils.py

@@ -230,6 +230,22 @@ def build_cli_parser(operation=None):
             help="List of attribute names to retrieve, defaults to all "
                  "attributes")
     elif operation is Operation.LOCATE:
+        parser.add_option(
+            "--offset-items",
+            action="store",
+            type="int",
+            default=None,
+            dest="offset_items",
+            help="The number of matching secrets to skip."
+        )
+        parser.add_option(
+            "--maximum-items",
+            action="store",
+            type="int",
+            default=None,
+            dest="maximum_items",
+            help="The maximum number of matching secrets to return."
+        )
         parser.add_option(
             "-n",
             "--name",