Tests

Add some tests to this repository:

• hadolint for Dockerfiles
• shellcheck for bash and sh scripts
• yamllint for YAML files

Currently marking every job with allow_failure: yes, but if this is accepted, I guess the next step would be to fix the "problems" and remove those lines.

.gitlab-ci.yml

@@ -19,5 +19,5 @@ dockerfiles:
 
 yamllint:
   image: sdesbure/yamllint
-  script: "yamllint -d relaxed $(find . \\( -name '*.yml' -o -name '*.yaml' \\))"
+  script: "yamllint $(find . \\( -name '*.yml' -o -name '*.yaml' \\))"
   allow_failure: yes