/etc/shadow, /etc/group and /etc/gshadow PRIOR to package installation
to guarantee user/group ordering on the image and then to check for any
unexpected change to those files. (LP: #1332538)
Any change to either the initial set of users and groups or to the
post-package-install set will now be fatal to the image and will require
a manual update of the hardcoded user/group list contained in this new
chroot_early hook.
* Bump dependency on live-build accordingly.
* Update the setup_user hook to also take care of gshadow.
