Recreate the backup script with shell, AWK, reg and skopeo.

A few reasons. First of all, it doesn't require a running Docker daemon
instead outputting directly to a file (faster and saves space). Also,
the restore script will probably use skopeo so this the codebase is more
uniform. Without the Docker daemon it can run with lower privileges.
Lastly, it should work without setting the really high timeout that bugs
me a little.