If phase1.ssh_user isn't set, also try to use $USER.
If phase1.ssh_user isn't set, also try to use $USER.

If the .config file is missing phase1.ssh_user, we should still attempt
to explicitly use $USER@host to avoid the poorly documented default
behavior of gcloud looking up the user from the service account (which
is wrong, in prow's case):

https://github.com/kubernetes/kubeadm/issues/219

If $USER is unset, like it is in the "make docker-dev" environment, then
we can still fall back to omitting the "user@" portion of the ssh
command. But, this will make it a little friendlier to use in other
environments.

weaveworks/weave-kubernetes-anywhere,weaveworks/kubernetes-anywhere,rohitjogvmw/kubernetes-anywhere