VAX boot.fs: Fix owner/group/permissions for VAX's boot.fs (Jan-Benedict Glaw)

(Initial patch from Christos Zoulas.)  Don't create an archive based on local
permission bits and owner/group. Instead, feed a small manifest into `pax`
and let it to its work.

  NB: Don't also feed in an entry for the current directory ".", as `pax` will
then archive all files in the current directory, in `readdir()` order.

(christos)