Set env vars when creating the chroot to make the build env more similar to Debian's buildds
This MR:
- reworks https://gitlab.collabora.com/obs/obs-build/-/merge_requests/21 to set the
LC_ALL=C.UTF-8
when creating the chroot rather than only when actually building the package - cleans
TERM
to preventscreen
from tricking some packages to produce unexpectedly colored ouput - sets
TZ=UTC
for good measure