CommitFailedError when a new generation may have formed about faust

[vineetgoel]

I saw this again:

[2018-05-09 20:34:15,848: ERROR]: OffsetCommit failed for group risk-faust-v16 due to group error ([Error 27] RebalanceInProgressError: risk-faust-v16), will rejoin
[2018-05-09 20:34:15,849: ERROR]: [^--Consumer]: Committing raised exception: CommitFailedError('Commit cannot be completed since the group has already rebalanced and may have assigned the partitions to another member',)
Traceback (most recent call last):
  File "/home/robinhood/env/lib/python3.6/site-packages/aiokafka/consumer/group_coordinator.py", line 820, in commit_offsets
    loop=self._loop)
  File "/home/robinhood/env/lib/python3.6/site-packages/aiokafka/consumer/group_coordinator.py", line 940, in _do_commit_offsets
    raise first_error
kafka.errors.RebalanceInProgressError: [Error 27] RebalanceInProgressError: risk-faust-v16

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/robinhood/env/lib/python3.6/site-packages/faust/transport/drivers/aiokafka.py", line 460, in _commit
    await self._consumer.commit(commitable)
  File "/home/robinhood/env/lib/python3.6/site-packages/aiokafka/consumer/consumer.py", line 436, in commit
    yield from self._coordinator.commit_offsets(assignment, offsets)
  File "/home/robinhood/env/lib/python3.6/site-packages/aiokafka/consumer/group_coordinator.py", line 825, in commit_offsets
    "Commit cannot be completed since the group has already "
kafka.errors.CommitFailedError: CommitFailedError: Commit cannot be completed since the group has already rebalanced and may have assigned the partitions to another member

and app was stalling.

[vineetgoel]

https://github.com/robinhoodmarkets/faust/commit/5ed2ac87f54f1199878b8e49da696a43c3bff1fa