VMware: Supported images for copy image to volume

VMware VMDK driver supports only images in vmdk disk format
with bare container format for copy image to volume operation.
The vmdk type can be preallocated, sparse, streamOptimized or
thin. This patch adds these details to the config reference.

Change-Id: Id5c6fc5aa70e584982ac7eff79e882134f975822
Merge "VMware: Supported images for copy image to volume"