Get plugin volume type from VolumeSnapshotDataSpec
Get plugin volume type from VolumeSnapshotDataSpec

This PR modifies one more place to get supported volume type
from VolumeSnapshotDataSpec and then get plugin from it.

humblec/external-storage,childsb/external-storage,kubernetes-incubator/external-storage,humblec/external-storage,childsb/external-storage,kubernetes-incubator/external-storage,childsb/external-storage,humblec/external-storage,kubernetes-incubator/external-storage