concatenate message list as single string with line feed.

def print_msg(contentlist):
        # type: (Union[AnyStr, List[AnyStr], Tuple[AnyStr]]) -> AnyStr
        """concatenate message list as single string with line feed."""
        if isinstance(contentlist, list) or isinstance(contentlist, tuple):
            return '\n'.join(contentlist)
        else:  # strings
            if len(contentlist) > 1 and contentlist[-1] != '\n':
                contentlist += '\n'
            return contentlist