VMDK: creating streamOptimized subformat Creating streamOptimized subformat. Added subformat option 'streamOptimized', to create a image with compression enabled and each cluster with a GrainMarker. Signed-off-by: Fam Zheng <famcool@gmail.com> Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>