tests/functional/test_ppc_bamboo: Replace broken link with working assets

tests/functional/test_ppc_bamboo: Replace broken link with working assets

The old image that we used for testing the bamboo machine has disappeared
from the internet. Fortunately there is another kernel + initrd provided
by Cédric that can be used for testing this machine, too.

Reported-by: Stefan Hajnoczi <stefanha@gmail.com>
Suggested-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20250707184736.88660-1-thuth@redhat.com>
(cherry picked from commit 3b1cf40dd665a0c4c38bc339fea6eacf1742b46c)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>