SSH session multiplexer

[natesales]

Currently we're using libvirt-sshd which only allows a single SSH connection to the VM virtual serial console. It would be neat to implement a session mux so multiple sessions can access a VM console at once. This will also solve the problem of console sessions becoming stuck in connected state if your terminal doesn't exit gracefully.

[lanefu]

I feel like borrowing from https://github.com/tmate-io/tmate would somehow get you there.