Mock of paramiko SFTP client is flakey

[Fizzadar]

This has been consistently frustrating CI for months and it's extremely annoying.

Thought #1386 would fix it but no. Now going to just disable the damn assertions to prevent the constant failures.

[wowi42]

Maybe time to move out of paramiko?

[Fizzadar]

Heh... #146. Worth re-investigating I think, given the slowly groing number of issues w/paramiko and upstream dev is v.slow. The library itself is also slow!

https://github.com/ParallelSSH/ssh2-python looks solid, and is supposed to implement the entire ssh2 library.