text: Title: `failed to garbage collect required amount of images. Wanted to free 473842483 bytes, but freed 0 bytes`
  Body: <!-- Please use this template while reporting a bug and provide as much info as possible. Not doing so may result in your bug not being addressed in a timely manner. Thanks!-->
  
  
  **What happened**: I've been seeing a number of evictions recently that appear to be due to disk pressure:
  ```yaml
  $$$ kubectl get pod kumo-go-api-d46f56779-jl6s2 --namespace=kumo-main -o yaml
  apiVersion: v1
  kind: Pod
  metadata:
    creationTimestamp: 2018-12-06T10:05:25Z
    generateName: kumo-go-api-d46f56779-
    labels:
      io.kompose.service: kumo-go-api
      pod-template-hash: "802912335"
    name: kumo-go-api-d46f56779-jl6s2
    namespace: kumo-main
    ownerReferences:
    - apiVersion: extensions/v1beta1
      blockOwnerDeletion: true
      controller: true
      kind: ReplicaSet
      name: kumo-go-api-d46f56779
      uid: c0a9355e-f780-11e8-b336-42010aa80057
    resourceVersion: "11617978"
    selfLink: /api/v1/namespaces/kumo-main/pods/kumo-go-api-d46f56779-jl6s2
    uid: 7337e854-f93e-11e8-b336-42010aa80057
  spec:
    containers:
    - env:
      - redacted...
      image: gcr.io/<redacted>/kumo-go-api@sha256:c6a94fc1ffeb09ea6d967f9ab14b9a26304fa4d71c5798acbfba5e98125b81da
      imagePullPolicy: Always
      name: kumo-go-api
      ports:
      - containerPort: 5000
        protocol: TCP
      resources: {}
      terminationMessagePath: /dev/termination-log
      terminationMessagePolicy: File
      volumeMounts:
      - mountPath: /var/run/secrets/kubernetes.io/serviceaccount
        name: default-token-t6jkx
        readOnly: true
    dnsPolicy: ClusterFirst
    nodeName: gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s
    restartPolicy: Always
    schedulerName: default-scheduler
    securityContext: {}
    serviceAccount: default
    serviceAccountName: default
    terminationGracePeriodSeconds: 30
    tolerations:
    - effect: NoExecute
      key: node.kubernetes.io/not-ready
      operator: Exists
      tolerationSeconds: 300
    - effect: NoExecute
      key: node.kubernetes.io/unreachable
      operator: Exists
      tolerationSeconds: 300
    volumes:
    - name: default-token-t6jkx
      secret:
        defaultMode: 420
        secretName: default-token-t6jkx
  status:
    message: 'The node was low on resource: nodefs.'
    phase: Failed
    reason: Evicted
    startTime: 2018-12-06T10:05:25Z
  ```
  Taking a look at `kubectl get events`, I see these warnings:
  ```
  $$$ kubectl get events
  LAST SEEN   FIRST SEEN   COUNT     NAME                                                                   KIND      SUBOBJECT   TYPE      REASON          SOURCE                                                         MESSAGE
  2m          13h          152       gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s.156e07f40b90ed91   Node                  Warning   ImageGCFailed   kubelet, gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s   (combined from similar events): failed to garbage collect required amount of images. Wanted to free 473948979 bytes, but freed 0 bytes
  37m         37m          1         gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s.156e3127ebc715c3   Node                  Warning   ImageGCFailed   kubelet, gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s   failed to garbage collect required amount of images. Wanted to free 473674547 bytes, but freed 0 bytes
  ```
  Digging a bit deeper:
  ```yaml
  $$$ kubectl get event gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s.156e07f40b90ed91 -o yaml
  apiVersion: v1
  count: 153
  eventTime: null
  firstTimestamp: 2018-12-07T11:01:06Z
  involvedObject:
    kind: Node
    name: gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s
    uid: gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s
  kind: Event
  lastTimestamp: 2018-12-08T00:16:09Z
  message: '(combined from similar events): failed to garbage collect required amount
    of images. Wanted to free 474006323 bytes, but freed 0 bytes'
  metadata:
    creationTimestamp: 2018-12-07T11:01:07Z
    name: gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s.156e07f40b90ed91
    namespace: default
    resourceVersion: "381976"
    selfLink: /api/v1/namespaces/default/events/gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s.156e07f40b90ed91
    uid: 65916e4b-fa0f-11e8-ae9a-42010aa80058
  reason: ImageGCFailed
  reportingComponent: ""
  reportingInstance: ""
  source:
    component: kubelet
    host: gke-kumo-customers-n1-standard-1-pree-0cd7990c-jg9s
  type: Warning
  ```
  There's actually remarkably little here. This message doesn't say anything regarding why ImageGC was initiated or why it was unable recover more space.
  
  **What you expected to happen**: Image GC to work correctly, or at least fail to schedule pods onto nodes that do not have sufficient disk space.
  
  **How to reproduce it (as minimally and precisely as possible)**: Run and stop as many pods as possible on a node in order to encourage disk pressure. Then observe these errors.
  
  **Anything else we need to know?**: n/a
  
  **Environment**:
  - Kubernetes version (use `kubectl version`): 
  ```
  Client Version: version.Info{Major:"1", Minor:"10", GitVersion:"v1.10.7", GitCommit:"0c38c362511b20a098d7cd855f1314dad92c2780", GitTreeState:"clean", BuildDate:"2018-08-20T10:09:03Z", GoVersion:"go1.9.3", Compiler:"gc", Platform:"darwin/amd64"}
  Server Version: version.Info{Major:"1", Minor:"10+", GitVersion:"v1.10.7-gke.11", GitCommit:"fa90543563c9cfafca69128ce8cd9ecd5941940f", GitTreeState:"clean", BuildDate:"2018-11-08T20:22:21Z", GoVersion:"go1.9.3b4", Compiler:"gc", Platform:"linux/amd64"}
  ```
  - Cloud provider or hardware configuration: GKE
  - OS (e.g. from /etc/os-release): I'm running macOS 10.14, nodes are running Container-Optimized OS (cos).
  - Kernel (e.g. `uname -a`): `Darwin D-10-19-169-80.dhcp4.washington.edu 18.0.0 Darwin Kernel Version 18.0.0: Wed Aug 22 20:13:40 PDT 2018; root:xnu-4903.201.2~1/RELEASE_X86_64 x86_64`
  - Install tools: n/a
  - Others: n/a
  
  <!-- DO NOT EDIT BELOW THIS LINE -->
  /kind bug