Improve error handling in RawSecureShellWS

[jsyrjala]

See https://github.com/NitorCreations/willow/blob/master/willow-servers/src/main/java/com/nitorcreations/willow/ssh/RawSecureShellWS.java#L102

Here session is closed in case of error (e.g. can't connect to port 22) but process continues on and tries to run e.g this

        run = new RawSentOutputTask(session, new BufferedInputStream(shell.getInputStream(), BUFFER_LEN));