SOLR-16992 Non-reproducible StreamingTest failures

[stillalex]

-- suggests CloudSolrStream concurency race condition

https://issues.apache.org/jira/browse/SOLR-16992

Description

Introduced a new method to deal with the executor task list work. it will wait for everything to complete and fully shut down. it will also attempt to throw the exception if one occurs, attaching all other exceptions to it.
refactored all previous uses to move to this common method.
Also, SolrClientCache is more strict about being closed

Open Questions

• where should the executor method live? it is now in a new class StreamExecutorHelper but it could easily move to ExecutorUtil, it is generic enough.

• I did not tackle adding 'closed' flags to all tuple stream impls. this might not strictly be needed to plug this gap. it could be a followup task given the amount of refactoring needed. thoughts?

Solution

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Tests

Please describe the tests you've developed or run to confirm this patch implements the feature or solves the problem.

Checklist

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• I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• I have created a Jira issue and added the issue ID to my pull request title.
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• I have developed this patch against the main branch.
• I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide