tests/acceptance: Test powernv machines

tests/acceptance: Test powernv machines

Fetch the OpenPOWER images to boot the powernv8 and powernv9 machines
with a simple PCI layout.

Cc: Cleber Rosa <crosa@redhat.com>
Cc: Philippe Mathieu-Daudé <philmd@redhat.com>
Cc: Wainer dos Santos Moschetta <wainersm@redhat.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210817093036.1288791-1-clg@kaod.org>