This works on gcloud (where the user is dynamically created by the tool),
but doesn't hold on other clouds (e.g. AWS).

The function in pkg/util now takes a user arg, and it is called only
from the e2e tests, which now check for env-var KUBE_SSH_USER, and then
fall back to the existing behaviour of env-var USER.

I am using this from Jenkins by directly setting the env-var:

export KUBE_SSH_USER=jenkins
...
hack/jenkins/e2e.sh