TestTruncate#testPurgeLogs fails on postcommit CI

[sijie]

BUG REPORT

1. Please describe the issue you observed:

• What did you do?

run TestTruncate#testPurgeLogs

• What did you expect to see?

The test should pass

• What did you see instead?

The test case failed with assertions of number of log segments after truncation.

Error Message
expected:<6> but was:<7>
Stacktrace
java.lang.AssertionError: expected:<6> but was:<7>
	at org.apache.distributedlog.TestTruncate.testPurgeLogs(TestTruncate.java:112)

Example runs can be found at: https://builds.apache.org/job/bookkeeper_postcommit_master_java8/org.apache.distributedlog$distributedlog-core/41/testReport/junit/org.apache.distributedlog/TestTruncate/testPurgeLogs/