none driver can't be used with non-Docker runtimes (looks for "docker" executable)

There is something wrong in the runtime detection of the precreate:

$ sudo minikube start --vm-driver=none --container-runtime=cri-o
😄  minikube v1.4.0 on Ubuntu 16.04
🤹  Running on localhost (CPUs=4, Memory=7800MB, Disk=138379MB) ...
🔄  Retriable failure: create: precreate: exec: "docker": executable file not found in $PATH
🤹  Running on localhost (CPUs=4, Memory=7800MB, Disk=138379MB) ...
🔄  Retriable failure: create: precreate: exec: "docker": executable file not found in $PATH
🤹  Running on localhost (CPUs=4, Memory=7800MB, Disk=138379MB) ...
🔄  Retriable failure: create: precreate: exec: "docker": executable file not found in $PATH
^C

For some reason it is calling the wrong Available function ?

func (r *Docker) Available() error {
	_, err := exec.LookPath("docker")
	return err
}

func (r *CRIO) Available() error {
	return r.Runner.Run("command -v crio")
}

And the docker runtime seems to be checking locally ? (I guess us using docker machine makes it always there)

It also forgot to look for crictl, but that is another story. (and interesting how this is regarded as a "retriable failure")