Return set of all partitions for topic (whether available or not)

        Arguments:
            topic (str): topic to check for partitions

        Returns:
            set: {partition (int), ...}

def partitions_for_topic(self, topic):
        """Return set of all partitions for topic (whether available or not)

        Arguments:
            topic (str): topic to check for partitions

        Returns:
            set: {partition (int), ...}
        """
        if topic not in self._partitions:
            return None
        return set(self._partitions[topic].keys())