Grub changes:
- trunk expects a static /boot/grub/grub.cfg
- 15.04 expects to run update-grub and rewrites /boot/grub/grub.cfg on each update with a custom /boot/grub/grub.cfg.d/09_snappy

Issues with r149 -> 154:
- 149 has dynamic generated grub.cfg, update-grub is called with the "other" /etc/ for grub to get the latest 09_linux code (which no longer exists)
- grub.cfg is stock grub.cfg from ubuntu itself, no more snappy custom config
- boot works but we always boot with the kernel in this grub.cfg because new snappy does not call update-grub anymore
- /boot/grub/{a,b} is empty
- booting only works because there is a legacy symlink  /{vmlinuz,initrd.img} *and* our grub.cfg supports that