[EE] Reduce diff with EE in `spec/helpers`

CE port: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26706

What does this MR do?

This reduces the CE/EE diff in spec/helpers.

What are the relevant issue numbers?

Related to https://gitlab.com/gitlab-org/gitlab-ee/issues/9506.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/10143.

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• EE specific content should be in the top level /ee folder