load header with engine id when engine dies in TaskScheduler

This ensures that the metadata dict on the *Client* has the engine_uuid of the engine on which the task failed.  It is identical to code elsewhere (Hub, Client) for identifying when engines die.

IPython/parallel/controller/scheduler.py

@@ -298,7 +298,13 b' class TaskScheduler(SessionFactory):'
                 raise error.EngineError("Engine %r died while running task %r"%(engine, msg_id))
             except:
                 content = error.wrap_exception()
-            msg = self.session.msg('apply_reply', content, parent=parent, subheader={'status':'error'})
+            # build fake header
+            header = dict(
+                status='error',
+                engine=engine,
+                date=datetime.now(),
+            )
+            msg = self.session.msg('apply_reply', content, parent=parent, subheader=header)
             raw_reply = map(zmq.Message, self.session.serialize(msg, ident=idents))
             # and dispatch it
             self.dispatch_result(raw_reply)