CNDB-13524: Properly shutdown executors, use test CFS in PendingAntiCompactionTest

[driftx]

What is the issue

In PendingAntiCompactionTest, the executors don't properly wait for completion to shutdown which causes shared state interference when the whole class is run.

What does this PR fix and why was it fixed

Waits for operations to complete, prefer test CFS over mock

[github-actions]

Checklist before you submit for review

• Make sure there is a PR in the CNDB project updating the Converged Cassandra version
• Use NoSpamLogger for log lines that may appear frequently in the logs
• Verify test results on Butler
• Test coverage for new/modified code is > 80%
• Proper code formatting
• Proper title for each commit staring with the project-issue number, like CNDB-1234
• Each commit has a meaningful description
• Each commit is not very long and contains related changes
• Renames, moves and reformatting are in distinct commits
• All new files should contain the DataStax copyright header instead of the Apache License one

[jtgrabowski]

How does this help to fix the problem for this test? Can you put the reasoning in the commit message or PR description?
As per the checklist

Each commit has a meaningful description

It looks like maybe only makeSSTables is meaningful here.

[driftx]

The primary fix is waiting for the executor to finish shutting down after shutdown() is invoked. When we don't do this it causes interference when the whole class is run.

makeSSTables gets around another shared state issue with MockSchema.newCFS but that is secondary to the executor problem.

[jtgrabowski]

Please see the attached check list, it contains the following point:

Proper title for each commit staring with the project-issue number, like CNDB-1234

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[cassci-bot]

❌ Build ds-cassandra-pr-gate/PR-1832 rejected by Butler

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1 new test failure(s) in 2 builds
See build details here

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Found 1 new test failures

Test	Explanation	Branch history	Upstream history
o.a.c.u.b.BinLogTest.testTruncationReleasesLogS...	regression	🔴🔵	🔵🔵🔵🔵🔵🔵🔵

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Found 1 known test failures