WIP azure: finalize azure image

The VHDs uploaded into azure must be sized a multiple of 1MB and the kernel
needs some custom boot parameters.

I still need to figure out dynamically sized images. Otherwise, we'll be pushing 8GiB over the network...
Yours will always round up, this code (assuming it works) will keep the image size if it is aligned. So running your code on an aligned image will add exactly 1MiB to the size. Perhaps add an assertion to build_image after image creation and vm_image_util after image resize that the file size is properly aligned.