vmdk: Fix next_cluster_sector for compressed write When the VMDK is streamOptimized (or compressed), the next_cluster_sector must not be incremented by a fixed number of sectors. Instead of this, it must be rounded up to the next consecutive sector. Fixing this results in much smaller compressed images. Signed-off-by: Radoslav Gerganov <rgerganov@vmware.com> Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>