Custom docker containers containing required bash scripts

Jobs should use custom images that contain all necessary scripts, instead of relying on the fact that the scripts exist in the target repository.

Related to hive#406 (closed)

.gitlab-ci.yml

@@ -111,6 +111,8 @@ build_docker_dind_image:
     DOCKER_DRIVER: overlay2
     DOCKER_TLS_CERTDIR: "/certs"
     BUILD_TARGET: "docker-dind"
+  before_script:
+    - !reference [.build_docker_image, before_script]
   script:
     - !reference [.build_docker_image, script]
   rules: