Start install-ssh-keys early
Start install-ssh-keys early

Coreos runs `coreos-cloudinit` to start each systemd service
sequentially and waits for service to be started before starting the
next one. This means that the `install-kube-system.service` blocks
`install-ssh-keys.service` until the API server is up.

Solution is to start the `install-ssh-keys.service` before
`install-kube-system.service`.

zalando-incubator/kubernetes-on-aws,zalando-incubator/kubernetes-on-aws,zalando-incubator/kubernetes-on-aws