jclouds-sshj doesn't handle getExitStatus returning null

In the SshjSshClient ExecConnection.create function, this line:

            int errorStatus = output.getExitStatus();

Does not currently handle the case when output.getExitStatus() is null, which is a valid return value according to SSHJ's JavaDocs. It's possible that the command needs to be explicitly closed before calling getExitStatus: https://github.com/hierynomus/sshj/issues/114.