Allow support for no kubernetes installtion

Currently, `kubernetes version` is required parameter and since it is [mutually exclusive](https://github.com/kubernetes/minikube/blob/master/cmd/minikube/cmd/start.go#L1652) with start arg `--no-kubernetes` it isn't possible to setup non kubernetes installation. It would be great to have that for users who are only interested in underlying container runtimes. 