Running out of disk should set cluster status to 507 (Insufficient Storage)

[tstromberg]

Related to #9024

If /var is full, it should be addressed in minikube status --layout=cluster -o json.

docker@minikube:~$ df -h
Filesystem      Size  Used Avail Use% Mounted on
overlay         7.9G  7.8G     0 100% /
tmpfs            64M     0   64M   0% /dev
tmpfs           2.0G     0  2.0G   0% /sys/fs/cgroup
shm              64M     0   64M   0% /dev/shm
/dev/vda1       7.9G  7.8G     0 100% /var
tmpfs           2.0G  8.5M  2.0G   1% /run
tmpfs           2.0G   12K  2.0G   1% /tmp
/dev/root       390M  390M     0 100% /usr/lib/modules
tmpfs           5.0M     0  5.0M   0% /run/lock

Everything looks OK, but it isn't:

% minikube status --layout=cluster -o json | jq                                                                                                                                  {
  "Name": "minikube",
  "StatusCode": 200,
  "StatusName": "OK",
  "Step": "Done",
  "StepDetail": "🏄  Done! kubectl is now configured to use \"minikube\"",
  "BinaryVersion": "v1.12.2",
  "Components": {
    "kubeconfig": {
      "Name": "kubeconfig",
      "StatusCode": 200,
      "StatusName": ""
    }
  },
  "Nodes": [
    {
      "Name": "minikube",
      "StatusCode": 200,
      "StatusName": "OK",
      "Components": {
        "apiserver": {
          "Name": "apiserver",
          "StatusCode": 200,
          "StatusName": "OK"
        },
        "kubelet": {
          "Name": "kubelet",
          "StatusCode": 200,
          "StatusName": "OK"
        }
      }
    }
  ]
}

Ideally, I would like to see both the node and cluster state populated with something like this when completely full:

  "StatusCode": 507,
  "StatusName": "INSUFFICIENT_STORAGE",
  "StatusDetail": "/var is out of disk space"

or if it's nearly out of space:

  "StatusCode": 203,
  "StatusName": "WARNING",
  "StatusDetail": "/var is almost of disk space (90%)"

Doing so via kubelet DiskPressure check would be ideal, but if need be, we can use minikube ssh to simulate this check initially.

[afbjorklund]

Related to #3574