Improve login name for test user

When logged in as the test user account, the name is an email address `dominic.oramtest.client@diamond.ac.uk-70414`. This is a bit confusing as it looks a bit like you're logged in as @DominicOram, it's also inconsistent with the usual behaviour which shows your fedID. Probably if it could show your name in both cases this would be best.

Start by locating the frontend entry point that renders the logged-in test user's name, then compare it with the existing display path that shows a fedID. Update the displayed value so the test user shows a name consistently rather than the email-like address, and verify both login cases in the UI.

Written by the indexing model from the issue text.