Ensure hostname + timezone changes are applied immediately.

Re #15

• run hostname command on updated /etc/hostname to apply change immediately
• run timedatectl after setting timezone, but only if CHROOT environment variable not set (NB: this is because timedatectl doesn't work in chroot environments, so blocks testing there; in fact, we could probably replace with simple timedatectl calls some more hacks that so far only were done to be workable under chroot testing conditions …?)