bundle2: stop capturing output for ssh again This backout 36111f98f23d since we can have real time output with ssh again. The tests change is not backed-out because it was a test output fix.

sshpeer: use the doublepipe object for the server to client channel This restores real-time output from ssh server while waiting for protocol data sent by the server.

sshpeer: introduce a "doublepipe" class This class is responsible for ensuring we still process the server output streamed through the ssh's 'stderr' pipe during the initial wait for other protocol streams. It currently only works on posix system because of its use of 'select.select'.