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>