Automatic merge from submit-queue (batch tested with PRs 50068, 52406, 52394, 48551, 52131). 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>..
Implement bulk polling of volumes for vSphere
This PR implements bulk polling of volumes - BulkVerifyVolumes() API for vSphere.
With the existing implementation, vSphere makes multiple calls to VC to check if the volume is attached to a node. If there are "N" volumes attached on "M" nodes, vSphere makes "N" VCenter calls to check if the volumes are attached to VC for all "N" volumes. Also, by default Kubernetes queries if the volumes are attached to nodes every 1 minute. This will substantially increase the number of calls made by vSphere cloud provider to vCenter.
Inorder to prevent this, vSphere cloud provider implements the BulkVerifyVolumes() API in which only a single call is made to vCenter to check if all the volumes are attached to the respective nodes. Irrespective of the number of volumes attached to nodes, the number of vCenter calls will always be 1 on a query to BulkVerifyVolumes() API by kubernetes.
@rohitjogvmw @divyenpatel @luomiao
```release-note
BulkVerifyVolumes() implementation for vSphere
```
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