There are several Kubernetes version checks done in for example pkg/config/defaults.go, either if cfg.DevCluster || utils.CheckVersionConstraint(cfg.KubernetesVersion, ">=1.8.0") or if !cfg.DevCluster && utils.CheckVersionConstraint(cfg.KubernetesVersion, "<1.8.0"). In pkg/nspawntool/kubeadm.go the check is used a little differently like if !utils.CheckVersionConstraint(cfg.KubernetesVersion, "<1.8").

Those patterns are basically error-prone, so I think we should make them somehow general and consistent. We could write a helper to simplify it.

See also #222 (comment)