[ENH] Add 2FA handling in zmq/ssh/tunnel.py

[dmanikowski-reef]

Hi guys,
I was investigating this issue from IPython regarding 2-factor authentication:
ipython/ipython#10934
and finally reached the pyzmq code.
My guess is that https://github.com/zeromq/pyzmq/blob/master/zmq/ssh/tunnel.py file is the best place to implement this feature.

As soon as you confirm that I'm right, I'll try to implement this :)

[minrk]

That sounds right! It's fine to do it here, but it could also be appropriate to take this opportunity to fork the implementation into jupyter_client itself, which gets releases more often and uses this code more than most.

[dmanikowski-reef]

Hm - so what's on your mind is that we should move the whole ssh tunneling straight to IPython?