Fixes for Auto DevOps QA specs

What does this MR do?

Fixes 2 problems with QA:

1. The domain name setting was not doing anything (as far as I could tell). Now we set the input and save the form
2. The waiting logic on the build page was flaky or just not really working. Waiting for the spinner to not be present seemed to not work and we were regularly still seeing the spinner in our build failure screenshots https://gitlab.com/gitlab-org/gitlab-qa/-/jobs/161759351

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated via this MR
• [-] Documentation reviewed by technical writer or follow-up review issue created
• [-] Tests added for this feature/bug
• [-] Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• [-] Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer