Require Dockerfile and shellcheck jobs to succeed

YAML is still allowed to fail because there's a pending problem in our custom
rosdep definition file.

.gitlab-ci.yml

 shellcheck:
   image: koalaman/shellcheck-alpine
   script: 'shellcheck deploy/base/ros_entrypoint.bash scripts/*sh'
-  allow_failure: yes
 
 # The ignored rules in hadolint checks are
 # DL3006 Always tag the version of an image explicitly
@@ -17,7 +16,6 @@ dockerfiles:
     - hadolint --ignore DL3006 --ignore DL3008 deploy/base/Dockerfile || RET=1
     - hadolint --ignore DL3006 --ignore DL3008 deploy/dev/Dockerfile || RET=1
     - exit $RET
-  allow_failure: yes
 
 yamllint:
   image: sdesbure/yamllint