netty leak detector logs "LEAK: HashedWheelTimer.release() was not called before it's garbage-collected." in AuditorElector-related unit tests

[dlg99]

BUG REPORT

1. Please describe the issue you observed:

related to Issue #1610

• What did you do?

Ran bookkeeper-server unit tests with paranoid leak detector

• What did you expect to see?

no leaks

• What did you see instead?

ERROR - [Time-limited test:Slf4JLogger@171] - LEAK: HashedWheelTimer.release() was not called before it's garbage-collected. See http://netty.io/wiki/reference-counted-objects.html for more information.
Recent access records:
Created at:
io.netty.util.HashedWheelTimer.(HashedWheelTimer.java:272)
io.netty.util.HashedWheelTimer.(HashedWheelTimer.java:216)
io.netty.util.HashedWheelTimer.(HashedWheelTimer.java:195)
org.apache.bookkeeper.client.BookKeeper.(BookKeeper.java:484)
org.apache.bookkeeper.client.BookKeeper.(BookKeeper.java:380)
org.apache.bookkeeper.replication.Auditor.initialize(Auditor.java:142)
org.apache.bookkeeper.replication.Auditor.(Auditor.java:123)
org.apache.bookkeeper.replication.AuditorElector$3.run(AuditorElector.java:276)
java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
java.util.concurrent.FutureTask.run(FutureTask.java:266)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
java.lang.Thread.run(Thread.java:748)

Got this in logs of
org.apache.bookkeeper.replication.AuditorLedgerCheckerTest
org.apache.bookkeeper.replication.AuditorPeriodicCheckTest
org.apache.bookkeeper.server.http.TestHttpService