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
+
+dockerfiles:
+  image: hadolint/hadolint:latest-debian
+  script:
+    - RET=0
+    - hadolint deploy/base/Dockerfile || RET=1
+    - hadolint deploy/dev/Dockerfile || RET=1
+    - exit $RET
+  allow_failure: yes
+
+yamllint:
+  image: sdesbure/yamllint
+  script: "yamllint $(find . \\( -name '*.yml' -o -name '*.yaml' \\))"
+  allow_failure: yes