docker testing should use noninteractive mode for installing

[ReimarBauer]

In my docker build for stable I run into

Configuring tzdata
------------------

Please select the geographic area in which you live. Subsequent configuration
questions will narrow this down by presenting a list of cities, representing
the time zones in which they are located.

The solution was to add:

ARG DEBIAN_FRONTEND=noninteractive
ENV TZ=Europe/Berlin

We do have for these images slightly different ubuntu packages compared to testing. But that whould also improve the testing setup.

[ReimarBauer]

This is on hold because

#2298

and not needed afterward