Automatic merge from submit-queue

Explicitly set CLOUDSDK_CONFIG override early in e2e-runner

I'm guessing this is why a number of gci-on-gke builds started failing after https://github.com/kubernetes/test-infra/pull/432 was merged - we're overriding the gcloud configuration location from the default, so the activated service account no longer works. Previously we did this service activation late, but after we'd overridden the value.

I've changed it to explicitly set to a known-good value every time at the very start.

cc @vishh @maisem @spxtr @fejta