grub2: Initial experimental support for Grub 2

Signed-off-by: Euan Harris <euan.harris@citrix.com>
grub2: Handle single quoted GRUB_DEFAULT

Signed-off-by: Euan Harris <euan.harris@citrix.com>
grub2: If we couldn't read GRUB_DEFAULT, assume first kernel

Signed-off-by: Euan Harris <euan.harris@citrix.com>
Merge pull request #22 from euanh/debian-experimental

grub2: Initial experimental support for Grub 2