Problems are hard enough to debug in a jailed kit process inside
a docker image; provide some visual feedback via stderr.

Change-Id: I54b0a21c1375be2acc9da0bbacf959a419471b08
Reviewed-on: https://gerrit.libreoffice.org/45256Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>