Add problem ID and exit code for "Ensure your system has enough CPUs. The minimum allowed is 2 CPUs"

[jtzwu]

Steps to reproduce the issue:

1. Run minikube start on a default Google Cloud Compute VM with 1 cpu with --output=json
2. Get the error {"data":{"exitcode":"64","message":"Ensure your system has enough CPUs. The minimum allowed is 2 CPUs.\n"},"datacontenttype":"application/json","id":"507528d8-0e85-47bb-a2d1-08b41d868683","source":"https://minikube.sigs.k8s.io/","specversion":"1.0","type":"io.k8s.sigs.minikube.error"}

gcloud needs a machine readable error code that matches 1-to-1 with the message for this so it can understand what the error was without parsing the message.