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...
The key piece is the `alignment` field in disk_layout.json is used to adjust both the alignment of partitions and the end of the disk. The current value is `2048` blocks or 1MiB