Tidy up secret key names

This contains only the changes needed to make the specs in !905 (merged) pass. Its target is the source branch of this MR, not master!

While adding this, I had to change a couple of specs, but none in a major way: https://gitlab.com/gitlab-org/omnibus-gitlab/commit/e6256afd44ac3bdaa6dc63a5a75164c88b3124a9