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

+shellcheck:
+  image: koalaman/shellcheck-alpine
+  script: 'shellcheck deploy/base/ros_entrypoint.bash scripts/*sh'
+  allow_failure: yes