In TestHDFSServerPorts.testBackupNodePorts, there are two attempts at starting backup node.
1) It binds namenode backup address with 0:
2) It sets namenode backup address with an available port X.
3) It fails rightfully due to using the same http address as active namenode.
1) It tries to reuse port X as namenode backup address.
2) It fails to bind to X because Windows does not release port X properly after Attempt 1 fails.