the final message for mult-checks

        arguments:
            msglevels: an array of all desired levels (ex: [CRITICAL, WARNING])
            joiner: string used to join all messages (default: ', ')

        returns:
            one-line message created with input results
            or None if there are none

def get_message(self, msglevels=None, joiner=None):
        """
        the final message for mult-checks

        arguments:
            msglevels: an array of all desired levels (ex: [CRITICAL, WARNING])
            joiner: string used to join all messages (default: ', ')

        returns:
            one-line message created with input results
            or None if there are none
        """
        messages = []
        if joiner is None:
            joiner = ', '
        if msglevels is None:
            msglevels = [OK, WARNING, CRITICAL]
        for result in self._results:
            if result.code in msglevels:
                messages.append(result.message)
        return joiner.join([msg for msg in messages if msg])