split it into multiple jobs after removing shared running

.gitlab-ci.yml

+stages:
+  - build
+  - test
+  - push
+
 before_script:
   - docker info
 
-refresh_image:
+build_image:
+  stage: build
   script:
     - docker build -t registry.cybbh.space/courseware-as-code/courseware-builder/container .
+  only:
+    - master
+
+test_image:
+  stage: test
+  script:
     - docker run registry.cybbh.space/courseware-as-code/courseware-builder/container /opt/course_builder/tests.sh
+  only:
+    - master
+
+push_image:
+  stage: push
+  script:
     - docker login -u "${DOCKER_LOGIN_USER}" -p "${DOCKER_LOGIN_PASS}" registry.cybbh.space
     - docker push registry.cybbh.space/courseware-as-code/courseware-builder/container
+    - rm ~/.docker/config.json
   only:
     - master