add `kafka_cluster` attribute to KafkaIntegrationTestCase
add `kafka_cluster` attribute to KafkaIntegrationTestCase

yungchin/pykafka,yungchin/pykafka,sontek/pykafka,aeroevan/pykafka,sammerry/pykafka,fortime/pykafka,benauthor/pykafka,wikimedia/operations-debs-python-pykafka,thedrow/samsa,jofusa/pykafka,benauthor/pykafka,wikimedia/operations-debs-python-pykafka,sammerry/pykafka,fortime/pykafka,jofusa/pykafka,benauthor/pykafka,appsoma/pykafka,appsoma/pykafka,vortec/pykafka,thedrow/samsa,vortec/pykafka,sontek/pykafka,tempbottle/pykafka,thedrow/samsa,tempbottle/pykafka,wikimedia/operations-debs-python-pykafka,aeroevan/pykafka