ssh's error output went to a pipe that nobody read while the console ran:
once it filled, ssh stopped and the console froze. It now goes to a
temporary file, read when the tunnel closes. Closing waits five seconds
for ssh to end and then kills it, instead of waiting for ever. The Tunnel
holds the ssh process and its error file together.
- The tunnel is `ssh -W` to the console's address or Unix socket: the
compute needs no nc and runs no shell. The old tunnel, copied from
virt-manager, built a shell script with the console's address and socket
path in it and eval'd it on the compute, and always passed "-p 22",
overriding a Port in the SSH configuration.
- On an SSH compute the console always goes through the tunnel, also when
it listens on a network address: it was sent there unencrypted.
- ssh never prompts (BatchMode) and gives up connecting after 10 seconds;
when it fails, what it said is logged. The tunnel ends with the session.
