Automatic merge from submit-queue

Expose PVC metrics via kubelet prometheus

This depends on https://github.com/kubernetes/kubernetes/pull/51448, opening early though. second commit is mine and mostly a copy/paste job.

implements metrics listed in here https://github.com/kubernetes/community/pull/855 following method here https://github.com/kubernetes/community/pull/930#issuecomment-325509736

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: https://github.com/kubernetes/features/issues/363

**Special notes for your reviewer**:

**Release note**:

```release-note
PersistentVolumeClaim metrics like "volume_stats_inodes" and "volume_stats_capacity_bytes" are now reported via kubelet prometheus
```