VMwareVCDriver Fix sparse disk copy error on spawn

The same approach of calling VirtualDiskManager.CopyVirtualDisk
without destination disk spec in the cluster driver for fixing 1184807
turns out to work for copying a sparse disk as well because vCenter's behavior
for specless copy is to do the reasonable thing of converting a sparse disk to
thin-provisioned, and a flat disk to preallocated.

Tests done:

Verified using tempest that sparse/thin/preallocated image types deploys
properly through the cluster driver. Tempest output to be included in
the review comments.

Fixes bug 1171226

Change-Id: I6c48866e06c2aa656c89848564f3262fb7b79039
Merge "VMwareVCDriver Fix sparse disk copy error on spawn"