QA E2E test logging/results when tests are run in parallel

When we run the QA E2E tests in parallel, we'll need to be sure we report test results in a useful, convenient way (including logging and artifacts, which help us understand the results).

The way tests results and logs are currently displayed might be sufficient for a first iteration. This aim of this issue is to determine if that's the case, and if not, to come up with something suitable.

This will depend on how we end up using parallel jobs and Knapsack, so https://gitlab.com/gitlab-org/gitlab-ce/issues/61215 should be completed first.