Log out in after all hook

What does this MR do?

Logs out in an after(:all) hook so that subsequent tests can login.

See https://gitlab.com/gitlab-org/quality/nightly/issues/103#note_176505015

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• [-] Separation of EE specific content