Some ciphers and key sizes created on-disk metadata that cannot be used.
Use the same test for length-preserving cipher as LUKS1.
Also check if key for integrity algorithm is not too small.
Fixes#373.
Kernel could reject HMAC without a key during format, we must set a key here as well.
Because there is no data area (device size is 8 sectors), it is actually never used,
so we can use zeroed key here.
The real HMAC key is used later during device activation with the real size.
The dm-integrity target is intended to be used for authenticated
encryption through LUKS and dm-crypt.
It can be used in standalone as well; for this use case there
is a simple configuration utility called integritysetup
(similar to veritysetup to dm-verity).
