bug#19190: Cannot boot with encrypted root

[Duncan Keall]

Here's what I've found using a very similar setup to Nikita and after
receiving the same error messages.

> Any message after entering the password prompt?

GRUB prints a single message "Slot 0 opened" and then it's into the
kernel boot logs. The first related message appears to be the
"ext2fs_check_if_mount..." one.

> Perhaps you could try running ‘cryptsetup’ by hand from the REPL.

I needed to replace "/bin/cryptsetup" with "/sbin/cryptsetup". After
that, cryptsetup accepted a password and printed these errors:

  device-mapper: table 253:0: crypt: Error allocating crypto tfm
  device-mapper: ioctl: error adding target to table
  device-mapper: reload ioctl on  failed: No such file or directory
  Failed to open temporary keystore device.
  device-mapper: remove ioctl on temporary-cryptsetup-149 failed: No
  such device or address

The return value was 256, and afterwards /dev/mapper/main still did not
exist.