Fixed issue saving tasks.

The Eve hook that added 'parent_info' caused this issue, as the validation
fails when saving a document that contains this. The easiest fix was to
prefix it with an underscore, so that the SDK automatically strips it
before saving.

attract/tasks/eve_hooks.py

@@ -32,7 +32,7 @@ def fetch_task_parent_info(node):
         return
 
     parent.pop('_id')  # always there, but also already included in the node.
-    node['parent_info'] = parent
+    node['_parent_info'] = parent
 
 
 def fetch_tasks_parent_info(nodes):