MINOR: Include exception objects when logging group coordinator errors

[squah-confluent]

...so that we capture stack traces for these errors.

[squah-confluent]

I've been trying to investigate some errors in group coordinator loading/unloading and the lack of stack traces is getting in the way. eg.

[GroupCoordinator id=2] Failed to unload metadata for __consumer_offsets-4 with epoch OptionalInt[5] due to java.lang.IllegalStateException.
...
[GroupCoordinator id=2] Failed to load metadata from __consumer_offsets-4 with epoch 10 due to java.lang.RuntimeException: Replaying record CoordinatorRecord(key=ConsumerGroupCurrentMemberAssignmentKey(groupId='...', memberId='ZxHk7W53S_aHFdpxYc-_Jw'), value=ApiMessageAndVersion(ConsumerGroupCurrentMemberAssignmentValue(memberEpoch=854659, previousMemberEpoch=854633, state=0, assignedPartitions=[TopicPartitions(topicId=9lL1aTMuSC22QAXsHgzhew, partitions=[1, 2]), TopicPartitions(topicId=RHKM682KQYyOfF1XsOSF1A, partitions=[0]), TopicPartitions(topicId=rKx9q1JmS1uP-ug_cj56ug, partitions=[0]), TopicPartitions(topicId=I7EtFwesTRubnj-VHClqbQ, partitions=[2]), TopicPartitions(topicId=ydAln6IUTZe-od9UUkn3rg, partitions=[2])], partitionsPendingRevocation=[]) at version 0)) from __consumer_offsets-4 at offset 3889549 with producer id -1 and producer epoch -1 failed..

EDIT: The first error is due to https://issues.apache.org/jira/projects/KAFKA/issues/KAFKA-19857.

[chia7712]

@squah-confluent thanks for this patch

[chia7712]

Because the whole exception ex is logged, changing ex.toString() to ex.getMessage() would eliminate a lot of redundant information in the log

[squah-confluent]

Thanks for reviewing! I've updated the PR to use getMessage instead.

[chia7712]

ditto