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attachdetach controller: attach volumes immediately when Pod's PVCs are bound
**What this PR does / why we need it**:
Let attachdetach controller to attach volumes immediately when Pod's PVCs are bound.
Current attachdetach controller calls `util.ProcessPodVolume` to add pod volumes into `desiredStateOfWorld` on these events:
- podAdd event
- podUpdate event
- podDelete event
- periodical `desiredStateOfWorldPopulator.findAndAddActivePod`
But if a pod is created with PVCs not bound, no volumes will be added into `desiredStateOfWorld` [because PVCs not bound](https://github.com/kubernetes/kubernetes/blob/v1.12.0-alpha.0/pkg/controller/volume/attachdetach/util/util.go#L99). When pv controller binds PVCs successfully, attachdetach controller will not add pod volumes immediately because it does not watch on PVC events.
It will wait until a pod update event is triggered (normally will not happen because no new status will be reported by kubelet) or `desiredStateOfWorldPopulator.findAndAddActivePod` is called (maybe 0~3 minutes later, see [timer configs](https://github.com/kubernetes/kubernetes/blob/v1.12.0-alpha.0/pkg/controller/volume/attachdetach/attach_detach_controller.go)).
In bad case, pod start time will be very long (~3 minutes + ~2 minutes (kubelet max exponential backoff)), for example: https://github.com/kubernetes/kubernetes/issues/64549#issuecomment-409440546.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes#64549
**Special notes for your reviewer**:
**Release note**:
```release-note
attachdetach controller attaches volumes immediately when Pod's PVCs are bound
```
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