MINOR: replace Thread.isAlive by Thread.is_alive for Python code (#11545)
MINOR: replace Thread.isAlive by Thread.is_alive for Python code (#11545)

Reviewers: Luke Chen <a747209bc9e65a9d7dd7589245c91b7bed721b13@gmail.com>, David Jacot <djacot@confluent.io>
apache/kafka,apache/kafka,lindong28/kafka,lindong28/kafka,guozhangwang/kafka,guozhangwang/kafka,apache/kafka,TiVo/kafka,TiVo/kafka,lindong28/kafka,guozhangwang/kafka,guozhangwang/kafka,lindong28/kafka,apache/kafka,TiVo/kafka,TiVo/kafka