'Create a ``ProcessNode`` that communicate over SSH.
:param bytes host: The hostname or IP.
:param int port: The port number of the SSH server.
:param bytes username: The username to SSH as.
:param FilePath private_key: Path to private key to use when talking to
SSH server.
:return: ``ProcessNode`` instance that communicates over SSH.'

@classmethod
def using_ssh(cls, host, port, username, private_key):

    return cls(initial_command_arguments=('ssh', '-q', '-i', private_key.path, '-l', username, '-o', 'StrictHostKeyChecking=no', '-o', 'ControlMaster=no', '-o', 'PreferredAuthentications=publickey', '-p', ('%d' % (port,)), host), quote=quote)
