move packages needed for all packages to seperate image

.gitlab-ci.yml

-image: stretch_website
+image: stretch_packages
 
 before_script:
   - export LANG=en_US.UTF-8
-  - echo "deb http://security.debian.org/debian-security stretch/updates main contrib non-free" >> /etc/apt/sources.list
-  - echo "deb-src http://security.debian.org/debian-security stretch/updates main contrib non-free" >> /etc/apt/sources.list
-  - sort /etc/apt/sources.list | uniq > sources.list.new
-  - mv sources.list.new /etc/apt/sources.list
-  - apt-get update
-  - apt-get install -y dpkg-dev quilt devscripts
   - export DEBIAN_FRONTEND="noninteractive"
   - export DEBIAN_PRIORITY="critical"
   - export DEBFULLNAME="FSMPI Admin-Team"
   - export DEBEMAIL="admin@fsmpi.rwth-aachen.de"
-#  - python3 -m venv venv
-#  - source venv/bin/activate
-#  - pip install wheel
-#  - pip install -r requirements.txt
-#  - mkdir -p ~/.ssh
-#  - echo $DEPLOY_KEY | base64 --decode > ~/.ssh/id_ed25519
-#  - chmod go-rw ~/.ssh/id_ed25519
-
 
 sssd:
   stage: build