apk2 includes uid/gid from build system

The apk archive includes uid/gid from the system it was build on. This is system dependent and differs if rootbld is used or not.

It would be nice to exclude that information to increase consistency. Especially for reproducible builds this needs to be consistent.

Tar has the options --owner=0 --group=0 which do standardize the uid/gid. The problem is that they also reset the username and groupname in the tar archive. These are needed by apk.

The issue could probably be fixed with the --owner-map and --group-map options but I haven't figured out how.