Merge pull request #3760 from edx/sarina/fix-split-test-child-id

Sarina/fix split test child

common/lib/xmodule/xmodule/split_test_module.py

@@ -159,7 +159,7 @@ class SplitTestModule(SplitTestFields, XModule):
 
             contents.append({
                 'group_id': group_id,
-                'id': child.id,
+                'id': child.location.to_deprecated_string(),
                 'content': rendered_child.content
             })