Cryptomount enhancements - revised

[John Lane <grub@jelmail.com>]

These patches provide extensions to the "cryptomount" command. There are five patches

 [PATCH 1/5] Cryptomount support LUKS detached header
 Support LUKS detached headers so that the header can be separated from the data payload, e.g. by storing on external removable media such as a USB key.

 [PATCH 2/5] Cryptomount support key files
 Support key files so that passphrase entry can be suppressed. The passphrase can be stored in a "key file" that can be stored, for example, on external removable media such as a USB key.

 [PATCH 3/5] cryptomount luks allow multiple passphrase attempts
 Allow a second attempt to enter a passphrase. If unlocking fails on the first attempt then the user is presented with the passphrase entry prompt again. If a key file is given that does not unlock the device then the user is given the opportunity to enter a passphrase.

 [PATCH 4/5] Cryptomount support plain dm-crypt
 Support plain dm-crypt mode. Allow plain volumes to be opened. This is largely a re-factoring of exisitng code to allow the crypto routines be used independently of LUKS.

 [PATCH 5/5] Cryptomount support for hyphens in UUID
 Support for hyphens in UUID. The "-u" option of cryptomount accepts a UUID. This option allows that to be delimited with hyphens so that the same format can be given to Grub as is passed to the Linux kernel boot options.


This is a revised patch set following feedback from patches sent on 16/6/15.

 grub-core/disk/cryptodisk.c | 382 ++++++++++++++++++++++++++++++++++++++++++++++++++--
 grub-core/disk/geli.c       |   9 +-
 grub-core/disk/luks.c       | 508 +++++++++++++++++++++++++--------------------------------------------
 include/grub/cryptodisk.h   |  18 ++-
 4 files changed, 581 insertions(+), 336 deletions(-)