Broken test: ExternalCompaction_1_IT.testPartialCompaction timing out

[dlmarion]

Test is succeeding on it's own, but when you run all the tests in the class it times out. In my runs testGetActiveCompactions runs before testPartialCompactions and both tests use the same group, QUEUE8 to execute compactions. Jstacking the Compactor process for that group, the Compactor is doing the following:

	at java.lang.Thread.sleep(java.base@11.0.23/Native Method)
	at org.apache.accumulo.test.functional.SlowIterator.next(SlowIterator.java:58)
	at org.apache.accumulo.server.compaction.FileCompactor.compactLocalityGroup(FileCompactor.java:535)
	at org.apache.accumulo.server.compaction.FileCompactor.call(FileCompactor.java:337)
	at org.apache.accumulo.compactor.Compactor$2.run(Compactor.java:573)
	at org.apache.accumulo.core.trace.TraceWrappedRunnable.run(TraceWrappedRunnable.java:52)
	at java.lang.Thread.run(java.base@11.0.23/Thread.java:829)

testGetActiveCompactions is the only test in the IT class that uses SlowIterator, and at the very end of the testGetActiveCompactions it cancels the compaction. The compaction cancellation must not be working.

[dlmarion]

I think #5026 caused this, but this test is not failing in 2.1 or main branches for some reason. The testGetActiveCompactions method creates a table with a lot of files (it's calling BatchWriter.flush in a loop). When the test cancels the user compaction, a bunch of system compactions are generated to get the number of files for the tablets below the threshold. Since the following test method is using the same compactor queue, the compactor process is busy compacting the tablets from the previous test and never gets around to compacting the tablets for the current test method, and it times out.