Automatic merge from submit-queue (batch tested with PRs 53234, 53252, 53267, 53276, 53107). If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Fix imagefs stats

Without this CRI stats based summary api won't work:
```console
$ curl localhost:10255/stats/summary
Internal Error: failed to get root cgroup stats: failed to get imageFs info: no imagefs label for configured runtime
```
With this PR, we could get summary api from cri-containerd now:
```console
$ curl localhost:10255/stats/summary
{
  "node": {
   "nodeName": "127.0.0.1",
   "startTime": "2017-09-23T06:26:49Z",
   "cpu": {
    "time": "2017-09-27T05:12:08Z",
    "usageNanoCores": 275510572,
    "usageCoreNanoSeconds": 11924595625329
   },
   "memory": {
    "time": "2017-09-27T05:12:08Z",
    "availableBytes": 27737075712,
    "usageBytes": 6028234752,
    "workingSetBytes": 3884470272,
    "rssBytes": 652304384,
    "pageFaults": 98472,
    "majorPageFaults": 87
   },
   "fs": {
    "time": "2017-09-27T05:12:08Z",
    "availableBytes": 75281231872,
    "capacityBytes": 104022159360,
    "usedBytes": 28724150272,
    "inodesFree": 12003204,
    "inodes": 12800000,
    "inodesUsed": 796796
   },
   "runtime": {
    "imageFs": {
     "time": "2017-09-27T05:12:00Z",
     "availableBytes": 75281231872,
     "capacityBytes": 104022159360,
     "usedBytes": 247732356,
     "inodesFree": 12003204,
     "inodes": 12800000,
     "inodesUsed": 6103
    }
   }
  },
  "pods": [
   {
    "podRef": {
     "name": "kube-dns-7797cb8758-qxkrz",
     "namespace": "kube-system",
     "uid": "4425b069-a342-11e7-ac90-42010af00002"
    },
    "startTime": "2017-09-27T05:11:23Z",
    "containers": [
     {
      "name": "kubedns",
      "startTime": "2017-09-27T05:11:24Z",
      "cpu": {
       "time": "1970-01-01T00:00:01Z",
       "usageCoreNanoSeconds": 154194917
      },
      "memory": {
       "time": "1970-01-01T00:00:01Z",
       "workingSetBytes": 7643136
      },
      "rootfs": {
       "time": "2017-09-27T05:12:00Z",
       "availableBytes": 75281231872,
       "capacityBytes": 104022159360,
       "usedBytes": 9,
       "inodesFree": 12003204,
       "inodes": 12800000,
       "inodesUsed": 32768
      },
      "logs": {
       "time": "2017-09-27T05:12:08Z",
       "availableBytes": 75281231872,
       "capacityBytes": 104022159360,
       "inodesFree": 12003204,
       "inodes": 12800000
      },
      "userDefinedMetrics": null
     },
     {
      "name": "dnsmasq",
      "startTime": "2017-09-27T05:11:24Z",
      "cpu": {
       "time": "1970-01-01T00:00:01Z",
       "usageCoreNanoSeconds": 114482989
      },
      "memory": {
       "time": "1970-01-01T00:00:01Z",
       "workingSetBytes": 7966720
      },
      "rootfs": {
       "time": "2017-09-27T05:12:00Z",
       "availableBytes": 75281231872,
       "capacityBytes": 104022159360,
       "usedBytes": 9,
       "inodesFree": 12003204,
       "inodes": 12800000,
       "inodesUsed": 28675
      },
      "logs": {
       "time": "2017-09-27T05:12:08Z",
       "availableBytes": 75281231872,
       "capacityBytes": 104022159360,
       "inodesFree": 12003204,
       "inodes": 12800000
      },
      "userDefinedMetrics": null
     },
     {
      "name": "sidecar",
      "startTime": "2017-09-27T05:11:24Z",
      "cpu": {
       "time": "1970-01-01T00:00:01Z",
       "usageCoreNanoSeconds": 140797580
      },
      "memory": {
       "time": "1970-01-01T00:00:01Z",
       "workingSetBytes": 7430144
      },
      "rootfs": {
       "time": "2017-09-27T05:12:00Z",
       "availableBytes": 75281231872,
       "capacityBytes": 104022159360,
       "usedBytes": 8,
       "inodesFree": 12003204,
       "inodes": 12800000,
       "inodesUsed": 28672
      },
      "logs": {
       "time": "2017-09-27T05:12:08Z",
       "availableBytes": 75281231872,
       "capacityBytes": 104022159360,
       "inodesFree": 12003204,
       "inodes": 12800000
      },
      "userDefinedMetrics": null
     }
    ],
    "volume": [
     {
      "time": "2017-09-27T05:12:03Z",
      "availableBytes": 15810760704,
      "capacityBytes": 15810772992,
      "usedBytes": 12288,
      "inodesFree": 3860043,
      "inodes": 3860052,
      "inodesUsed": 9,
      "name": "kube-dns-token-l2blr"
     }
    ]
   }
  ]
 }
```
Signed-off-by: Lantao Liu <lantaol@google.com>

```release-note
Fix the bug that query Kubelet's stats summary with CRI stats enabled results in error.
```