zfs: allow unlock multiple encrypted pools

[RinCat]

Added 2 new values for dozfs.

loadkeyall will use zfs load-key -a to ask all passphrases, not just root.

unifiedkey will try to use a single key to unlock all pools. It must be used with loadkeyall. It does not need to be able to unlock all pools, but it must be able to unlock the root pool.

Also unlock-zfs support -a for all pools, and -u for unified key.

Signed-off-by: Rin Cat (鈴猫) [email protected]