CI: run e2e tests on a dedicated node
Created by: chrismwendt
This runs e2e tests on a dedicated e2e testing node to avoid the contention problems of running in the same dind pod as builds, and the throughput problem of limiting concurrency to 1.
Peer commit https://github.com/sourcegraph/infrastructure/commit/d9b73eee437d7d027485ffa23802af9c0e9c996b