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...
Ah, I only noticed the 64KB alignment. There is a difference between disk_util and my extra glue though and I'm not certain where it comes from.