HDDS-8554. Thread pool size needs to be decreased in different order in ReplicationSupervisor

[adoroszlai]

What changes were proposed in this pull request?

ozone/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/replication/ReplicationSupervisor.java

Lines 164 to 165 in a455597

	tpe.setMaximumPoolSize(threadCount);
	tpe.setCorePoolSize(threadCount);

The above code works when increasing thread pool size, but fails when decreasing it, because maximum cannot be set to less than core. Seen in TestDecommissionAndMaintenance logs:

java.lang.IllegalArgumentException
	at java.util.concurrent.ThreadPoolExecutor.setMaximumPoolSize(ThreadPoolExecutor.java:1680)
	at org.apache.hadoop.ozone.container.replication.ReplicationSupervisor$Builder.lambda$build$1(ReplicationSupervisor.java:164)
	at org.apache.hadoop.ozone.container.replication.ReplicationSupervisor.nodeStateUpdated(ReplicationSupervisor.java:294)

Core pool size needs to be decreased first to satisfy preconditions.

https://issues.apache.org/jira/browse/HDDS-8554

How was this patch tested?

Added unit test. TestDecommissionAndMaintenance no longer logs this error.

[sodonnel]

LGTM - Good to see the decommission tests caught this, but bad the decommission tests are flaky so we don't trust them!

[adoroszlai]

Thanks @sodonnel for the review.