osbuild removed GRUB2_ROOT_FS_UUID from grubenv in 22d131a5. This broke
the Jenkins CI because it runs against osbuild master.
This commit fixes all the testcases and bumps the osbuild submodule
to version 13 that changed the GRUB2_ROOT_FS_UUID behaviour.
Requests to download.fedoraproject.org are redirected to a regional
mirror that is fairly close to the system that is making the request.
This could speed up downloads slightly since it avoids using the
Fedora proxies.
Signed-off-by: Major Hayden <major@redhat.com>