VMware ESX: Fixes vol clone & clone from snapshot

VMware ESX: Fixes vol clone & clone from snapshot

The driver was earlier performing create from a source volume and create from
a snapshot point by copying the source volume container folder.

This is not valid in case of vSAN datastore where the volume data is not a
'file' in the container folder unlike VMFS/NFS datastores. So copying folder
will only copy descriptor file and hence the source and cloned volume will
end up writing to the same data location, eventually corrupting it.

The fix is to copy only the VMDK file (descriptor + data) and not the entire
container folder. The implementation does the following:
1. Create a volume backing
2. Delete the current VMDK
3. Make a copy of source volume's VMDK file to the destination using virtual
   disk manager. In case of create from snapshot, we copy the VMDK file
   corresponding to the snapshot point.

Fixes bug: 1233034

Change-Id: I51c9870c11a6d66f9f47c1ad9aaa2abc3dd0533a