'Given a line with an Eliot message, it inserts the hostname
and the system name into the message
:param line: The line read from the tail output that was identified
as an Eliot message'

def parse_line(self, line):

    try:
        message = json.loads(line)
    except ValueError:
        message = dict(message=line)
    message[u'_HOSTNAME'] = self._host
    message[u'_PROCESS_NAME'] = self._service
    return message
