grub_install: work around intermittent missing loopback partitions

I am unsure exactly what situation is causing the loopback partition
device node to not exist when it is being mounted but this should help
work around the situation and log loudly about it so we can hopefully
figure out where to dig further.
vm_image_util: Enable new VMware OEM package.
disk_layout: Align disk sizes to both 1MB and cylinder boundaries.

The VHD disk format internally includes CHS addressing and qemu-img
respectfully aligns disk images to the common 16 heads 63 sectors
geometry when possible. This is unfortunate since images uploaded to
Azure must also be aligned to 1MB we normally do.

Since qemu-img doesn't have a way to handle this well right now adjust
our existing alignment logic to create disk images aligned to both.
disk_layout: adjust ROOT partition sizes to fill new alignment

The new disk size alignment left too much extra space at the end of the
disk which would lead to pointless resizing on first boot. Fill in the
extra space so that no more than 1MB is left unused.
Merge pull request #339 from marineam/hackery

Misc hackery
Merge branch 'master' of https://github.com/coreos/scripts