That message means that assertDirectoryDeleted failed to delete three files on the first attempt to delete the db_master directory (which is the master database used by the replication test I assume), but that it succeeded on the second attempt.
If assertDirectoryDeleted is unable to delete all files including the directory itself after the maximum number of attempts, it will fail the test.
I adjusted the priority to minor.
There is also DERBY-5386 for a different, but related, problem in the replication test. The code looks sound, but obviously something isn't quite right...