BROADCAST_URL of Kafka cluster not getting parsed -

[rohitswarke]

Issue: BROADCAST_URL for Kafka cluster doesn't get parsed correctly and throws KafkaConnectionError

Sample URL:
BROADCAST_URL = 'kafka://server1:port,server2:port,server3:port'

Description:
aiokafka client is using collect_hosts method of kafka.conn and while
kafka.conn.collect_hosts method collects a comma-separated set of hosts (host:port)
https://github.com/dpkp/kafka-python/blob/master/kafka/conn.py#L1485

In broadcaster._backends.kafka we are preparing bootstrap server by passing list of entire netloc string as shown below:
https://github.com/encode/broadcaster/blob/master/broadcaster/_backends/kafka.py#L13
self._servers = [urlparse(url).netloc]
If we tweak above line with below statement then it will support kafka cluster connection string:
self._servers = urlparse(url).netloc.split(',')

Do let me know your thoughts on this.