ISSUE-2665: ReadOnlyBookieTest is flaky

[sijie]

Original Issue: apache#2665

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BUG REPORT

Describe the bug

ReadOnlyBookieTest is flaky on current master branch

To Reproduce

mvn clean install -DskipTests
cd bookkeeper-server/
run a few times:
mvn test -Dtest=org.apache.bookkeeper.test.ReadOnlyBookieTest

[INFO] Running org.apache.bookkeeper.test.ReadOnlyBookieTest
[ERROR] Tests run: 6, Failures: 0, Errors: 1, Skipped: 0, Time elapsed: 31.14 s <<< FAILURE! - in org.apache.bookkeeper.test.ReadOnlyBookieTest
[ERROR] org.apache.bookkeeper.test.ReadOnlyBookieTest.testBookieContinueWritingIfMultipleLedgersPresent  Time elapsed: 4.151 s  <<< ERROR!
org.apache.bookkeeper.client.BKException$BKNotEnoughBookiesException: Not enough non-faulty bookies available
	at org.apache.bookkeeper.client.SyncCallbackUtils.finish(SyncCallbackUtils.java:83)
	at org.apache.bookkeeper.client.SyncCallbackUtils$SyncAddCallback.addComplete(SyncCallbackUtils.java:251)
	at org.apache.bookkeeper.client.AsyncCallback$AddCallback.addCompleteWithLatency(AsyncCallback.java:92)
	at org.apache.bookkeeper.client.PendingAddOp.submitCallback(PendingAddOp.java:431)
	at org.apache.bookkeeper.client.LedgerHandle.errorOutPendingAdds(LedgerHandle.java:1799)
	at org.apache.bookkeeper.client.LedgerHandle$5.safeRun(LedgerHandle.java:574)
	at org.apache.bookkeeper.common.util.SafeRunnable.run(SafeRunnable.java:36)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
	at java.base/java.lang.Thread.run(Thread.java:834)

[INFO]
[INFO] Results:
[INFO]
[WARNING] Flakes:
[WARNING] org.apache.bookkeeper.test.ReadOnlyBookieTest.testBookieContinueWritingIfMultipleLedgersPresent
[ERROR]   Run 1: ReadOnlyBookieTest.testBookieContinueWritingIfMultipleLedgersPresent » BKNotEnoughBookies
[INFO]   Run 2: PASS