Rather than use the round-robin mirror, use a fixe stable one.
We should not over-use this, but it seems the round-robin one is
simply too unstable for our tests.
Eventually, we want to use metalink here instead, but we need to
rework the file source first, so we can do that in a way that
does not make the tests dependent on the time/place the test
case was generated (currently the URL to a specific mirror ends
up pinned in the test-case).
Signed-off-by: Tom Gundersen <teg@jklm.no>
380029b572