tests: assign the storage servers to a fixed order which triggers a bug in new downlo...

tests: assign the storage servers to a fixed order which triggers a bug in new downloader every time this test is run (formerly this test would detect the bug in new-downloader only sporadically)
If you are investigating the bug in new-downloader, one way to investigate might be to change this ordering to a different fixed order (e.g. rotate by 4 instead of rotate by 5) and observe how the behavior of new-downloader differs in that case.