Comment 39 for bug 1996188

Revised patch posted in case anyone has time to look over Thanksgiving. This is not the final version. I had to move some code around because we weren't checking the format info for a image with container_format==compressed correctly (qemu-img info was being run on the gzip'd file, which would always report itself as 'raw' format. Also added a check to make sure the disk_format and what cinder detects as the image format matches, which I think is correct, but which may make some previously successful requests to create a volume from a source image to now fail.