Comment 10 for bug 2071734

I'm just realizing that this will re-open the data-file exposure if you hide a bad qcow in a glance image claiming to be another format. We won't know it's a qcow, won't safety-check it, and then will proceed to call qemu-img on it. I need to add in some code I had before that I removed to try to trim it down, but I'm realizing we still need it. It will use format-inspector's detect method to make sure we agree with what glance thinks it is (like we're doing below for qemu).

I'll get that respun and tested, it might not happen today with the holiday.