bug#21843: Generated grub.cfg does not support encrypted roots

[Andreas Enge]

What is needed are the following two lines at the beginning of grub.cfg:

insmod luks
cryptomount -u 1aa...

where 1aa... is the result of "cryptsetup luksUUID /dev/sda2".

So the logic outlined in my previous message works:
Determine the mapped-devices /dev/sdXY of type luks-device-mapping that
lead to a file-system with needed-for-boot? set to #t.
Using
   cryptsetup luksUUID /dev/sdXY
determine a corresponding uuid 12345...0.
If any such mapped-device exists, add
   insmod luks
as the first line of grub.cfg. For any such mapped-device, add a line
   cryptomount -u 12345...0
right after that.

To simplify the logic, we could also move the needed-for-boot? parameter
to mapped-device, or add such a parameter there.

Andreas