Refactor create service spec ## What does this MR do? Use let instead instance variables to cache create user operation. Union some example into one. ## Are there points in the code the reviewer needs to double check? ## Why was this MR needed? Time before: 1 minute 11.81 seconds Time after: 52.47 seconds - [x] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added - n/a [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md) - n/a API support added - Tests - n/a Added for this feature/bug - [x] All builds are passing - [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html) - [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides) - [x] Branch has no merge conflicts with `master` (if it does - rebase it please) - [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits) ## What are the relevant issue numbers? See merge request !7609
