LuceneIndexMaintenanceTest.ConcurrentStoreTest sometimes has timeouts

[ScottDugas]

For example:

LuceneIndexMaintenanceTest > concurrentStoreTest(boolean, boolean, boolean, int, long) > com.apple.foundationdb.record.lucene.LuceneIndexMaintenanceTest.concurrentStoreTest(boolean, boolean, boolean, int, long)[2] FAILED
    java.util.concurrent.CompletionException: java.lang.RuntimeException: Failed merge at iteration 16
        at java.base/java.util.concurrent.CompletableFuture.encodeThrowable(CompletableFuture.java:314)
        at java.base/java.util.concurrent.CompletableFuture.completeThrowable(CompletableFuture.java:319)
        at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1702)
        at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1692)
        at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:290)
        at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1020)
        at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1656)
        at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1594)
        at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:183)

        Caused by:
        java.lang.RuntimeException: Failed merge at iteration 16
            at com.apple.foundationdb.record.lucene.LuceneIndexMaintenanceTest$ConcurrentStoreTestRunner.mergeIndex(LuceneIndexMaintenanceTest.java:932)
            at com.apple.foundationdb.record.lucene.LuceneIndexMaintenanceTest$ConcurrentStoreTestRunner.get(LuceneIndexMaintenanceTest.java:903)
            at com.apple.foundationdb.record.lucene.LuceneIndexMaintenanceTest$ConcurrentStoreTestRunner.get(LuceneIndexMaintenanceTest.java:849)
            at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1700)
            ... 6 more

            Caused by:
            com.apple.foundationdb.record.RecordCoreException
                at app//com.apple.foundationdb.record.provider.foundationdb.FDBExceptions.wrapException(FDBExceptions.java:219)
                at app//com.apple.foundationdb.record.provider.foundationdb.FDBDatabase.lambda$new$0(FDBDatabase.java:172)
                at app//com.apple.foundationdb.record.provider.foundationdb.FDBDatabase.asyncToSync(FDBDatabase.java:1098)
                at app//com.apple.foundationdb.record.provider.foundationdb.FDBDatabaseRunnerImpl.asyncToSync(FDBDatabaseRunnerImpl.java:308)
                at app//com.apple.foundationdb.record.provider.foundationdb.OnlineIndexer.asyncToSync(OnlineIndexer.java:818)
                at app//com.apple.foundationdb.record.provider.foundationdb.OnlineIndexer.mergeIndex(OnlineIndexer.java:552)
                at app//com.apple.foundationdb.record.lucene.LuceneIndexMaintenanceTest.explicitMergeIndex(LuceneIndexMaintenanceTest.java:1057)

                Caused by:
                com.apple.foundationdb.record.LoggableTimeoutException
                    at app//com.apple.foundationdb.record.provider.foundationdb.FDBDatabase.asyncToSync(FDBDatabase.java:1098)
                    ... 4 more

                    Caused by:
                    java.util.concurrent.TimeoutException
                        at java.base/java.util.concurrent.CompletableFuture.timedGet(CompletableFuture.java:1892)
                        at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2027)
                        at com.apple.foundationdb.record.provider.foundationdb.FDBDatabase.asyncToSync(FDBDatabase.java:1091)
                        ... 4 more