Automatic merge from submit-queue (batch tested with PRs 51441, 51356, 51460)
Don't update pvc.status.capacity if pvc is already Bound
As discussed here https://github.com/kubernetes/community/pull/657#discussion_r128008128, in order for `pvc.status.Capacity < pv.Spec.Capcity` to be the mechanism for volume filesystem* resize, the pv controller should stop updating pvc.status.Capacity every resync period.
/assign @jsafrane
/sig storage
```release-note
NONE
```
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