letsencrypt-test job always passes

https://gitlab.com/gitlab-org/omnibus-gitlab/-/jobs/11817027218

The call to test.sh is failing, and exiting non-zero. But the rake task uses the system method to execute the script. The exit code is not checked, and so the job always passes.

This could feasibly be broken into two issues:

1. Fix the underlying issue as to why the job is failing
2. Fix the rake task to exit non-zero in case of failure.