Add convenience flag for reverse ssh tunnels

[oakreid]

SSH supports the creation of reverse tunnels using a very similar syntax to normal tunnels. From the man pages:

     -R [bind_address:]port:host:hostport
     -R [bind_address:]port:local_socket
     -R remote_socket:host:hostport
     -R remote_socket:local_socket
     -R [bind_address:]port

This PR adds a flag to the .tunnel() method of SshMachine that allows for easy creation of a reversed SSH tunnel

[henryiii]

Thanks! Didn't format or catch that time_ns was included, but doing that in #566.

[henryiii]

FYI, this is not picklable, so can't be forked. Why did this only matter on Python 3.10 + macOS? I have no idea. Anyway, moving it out of the test function should fix the problem.

[oakreid]

That's very strange. Thanks for cleaning that up!

[henryiii]

Think you could look into possibly making the test support forked multiprocessing? Not a big issue if not (the MP part is really due to the test needing both sides of the tunnel, not a normal occurrence).

[oakreid]

Yeah I can definitely look into it!