BookKeeperAdminTest.testDecommissionBookie is flaky

[sijie]

BUG REPORT

1. Please describe the issue you observed:

• What did you do?

run ci job

• What did you expect to see?

all tests should pass

• What did you see instead?

BookKeeperAdminTest.testDecommissionBookie failed.

https://builds.apache.org/job/bookkeeper-precommit-pullrequest/org.apache.bookkeeper$bookkeeper-server/336/testReport/junit/org.apache.bookkeeper.client/BookKeeperAdminTest/testDecommissionBookie/

[sijie]

Close this issue since it is an old issue. Will reopen if this test becomes flaky again.