Connect times out when server rejects initializing subsystem

[drieseng]

We currently do not check whether the request to initialize the subsystem is successful.

In case of SFTP, we try to send a SSH_FXP_INIT request wait for the remote window size to be adjusted if the server rejected the subsystem request.

Eventually the operation times out, and a SshOperationTimeoutException is thrown.

We need to check whether the request to initialize the subsystem is successful, and if not immediately throw an SshException and close the channel and SSH session.