Use docker for ci

Signed-off-by: Clemens John <clemens.john@openitb.com>

.gitlab-ci.yml

 ---
-# This needs runner infrastructure to be based on Docker (TODO)
-#
 variables:
   GIT_SUBMODULE_STRATEGY: recursive
 
@@ -9,8 +7,8 @@ stages:
 
 lint:
   stage: lint
-#  image: debian:latest
+  image: debian:latest
   tags:
-    - puppet
+    - docker
   script:
     - bash .lint/lint.sh