test-infra: ClusterLoader tests are failing to find scripts

All ClusterLoader tests are failing with the following error:

error starting /src/k8s.io/perf-tests/clusterloader/run-e2e.sh: fork/exec /src/k8s.io/perf-tests/clusterloader/run-e2e.sh: no such file or directory

See e.g.: https://k8s-gubernator.appspot.com/build/kubernetes-jenkins/logs/ci-perf-tests-e2e-gce-clusterloader/677

I spent some time trying to debug it and I realized, that in prow we are running scripts in “Local” mode (whereas in Jenkins we are running in “Docker” mode). As a result, the “–mount-path” flags doesn’t have any effect.

As a result, things like this: https://github.com/kubernetes/test-infra/blob/master/kubetest/e2e.go#L417

can’t be done universally, because we don’t really know the path.

I can workaround it in clusterloader test by attaching “/go” prefix and it will work, but that’s not a universal fix, and we will face exactly the same issue e.g. when we will be migrating “charts” job to prow.

We need to have some story for it.

@kubernetes/test-infra-maintainers