- Use an allocation of 65536 uids and gids to allow for POSIX-compliant
user owned namespaces.
- Don't allocate a uid/gid map to system users.
Unfortunately checking for --system isn't quite enough as some
distribution wrappers always call useradd without --system and take care
of choosing a uid and gid themselves, so also check whether the
requested uid/gid is in the user range.
This is taken from a patch I wrote for Ubuntu a couple years ago and
which somehow didn't make it upstream.
Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>
65c2617140