Code review comment for lp:~saviq/simplestreams/add-vhd-images

The patch here looks fine, but I wont merge it without someone on cpc team approval.

I do have the general dislike of Ubuntu publishing .vmdk and .qcow2 and
 .here-is-another-format-that-a-hypervisor-could-convert-from-the-open-standard-qcow2.

But that is my only objection, and based on the many formats we publish, we've decided not to use Ubuntu's leverage to help the industry with interoperability.