Automatic merge from submit-queue

Add volume operation metrics to operation executor and PV controller

This PR implements the proposal for high level volume metrics https://github.com/kubernetes/community/pull/809

**Special notes for your reviewer**:

~Differences from proposal:~ all resolved

~"verify_volume" is now "verify_volumes_are_attached" + "verify_volumes_are_attached_per_node" + "verify_controller_attached_volume." Which of them do we want?~

~There is no "mount_device" metric because the MountVolume operation combines MountDevice and mount (plugin.Setup). Do we want to extract the mount_device metric or is it okay to keep mountvolume as one? For attachable volumes, MountDevice is the actual mount and Setup is a bindmount + setvolumeownership. For unattachable, mountDevice does not occur and Setup is an actual mount + setvolumeownership.~

~PV controller metrics I did not implement following the proposal at all. I did not change goroutinemap nor scheduleOperation. Because provisionClaimOperation does not return an error, so it's impossible for the caller to know if there is actually a failure worth reporting. So I manually create a new metric inside the function according to some conditions.~

@gnufied 

I have tested the operationexecutor metrics but not provision & delete. Sample: 
![screen shot 2017-08-02 at 15 01 08](https://user-images.githubusercontent.com/13111288/28889980-a7093526-7793-11e7-9aa9-ad7158be76fa.png)


**Release note**:

```release-note
Add error count and time-taken metrics for storage operations such as mount and attach, per-volume-plugin.
```