chroot: userspec argument is not respected in chroot environment

[jfinkels]

Environment: Ubuntu 20.04, uutils main branch (git commit 6a8b766), GNU coreutils v8.30

Steps to reproduce:

sudo chroot --userspec=65534 / id -G

What happens now: uutils chroot outputs the ID of the root user

0

What I expected to happen: GNU chroot outputs the ID of the user given in the --userspec argument:

65534

Notes: this is causing a failure in the GNU test file tests/chroot/chroot-credentials.sh.