Only write sha to latest
Only write sha to latest

Instead of the path to the latest Packages.xz, makes migration and
parsing a bit easier

Signed-off-by: Appu Goundan <8b90a6cca43e83a08fc207ac57c01c50f0010120@google.com>

GoogleContainerTools/distroless,GoogleContainerTools/distroless,GoogleContainerTools/distroless