sos_comm closed after long waiting time.

[BoPeng]

After a notebook has been running for a long time (e.g. waiting for long tasks to complete), the frontend sos_comm can be disconnected for some reason, and the notebook becomes non-operable (e.g. %task would not get response). There should be someway for frontend to detect lost sos_comm and re-create one.

[BoPeng]

It appears that the sos_comm is ok but the ippub shell channel is missing, so it might be a problem with Jupyter, not SoS Notebook. We will have to investigate this more.