minikube status: show timeToStop only if it exists

[medyagh]

$ minikube status
minikube
type: Control Plane
host: Running
kubelet: Running
apiserver: Running
kubeconfig: Configured
timeToStop: Nonexistent

[medyagh]

so the idea is, if minikube is NOT scheduled to stop, it shouldn't bother to mention it in the status

instead of saying timeToStop: Nonexistent

[tharun208]

/assign