'Return the message of a log line.
If the line isn\'t from the log it will raise a ValueError
>>> line = \'[16:59:03] [INFO] fetching tables\'
>>> self._get_log_message(\'line\')
\'fetching tables\''

def _get_log_message(self, line):

    match = re.match('\\[[0-9:]+\\]    \\[\\w+\\]    (.+)$', line)
    if (match is None):
        raise ValueError('Incorrect    format    of    line')
    return match.group(1)
