QA: Fix: set initial password even if using admin credentials

What does this MR do?

In https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/21657 I added the ability to log in using admin credentials, but I didn't account for needing to change the initial password, which broke EE tests. This fixes that.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/quality/nightly/issues/10

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• 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