Change debian-stretch-build-dist to be based on debian-stretch-obs-latest instead of debian-stretch-build. The latter installs the nightly OBS repository now (as that is what we need for the TTCN-3 builds using debian-stretch-build), but debian-stretch-build-dist needs to install packages from OBS latest.
Fixes jenkins failures: The following packages have unmet dependencies: libasn1c-dev : Depends: osmocom-latest but it is not going to be installed ...
