Bug#910249: Bumping up encryption to AES-256 by default

[Jeremy Bicha]

I just uploaded libblockdev 2.20-7. Please check if it fixes your issue.

If it does, would you be interested in filing the unblock bug to get
the fix in to Debian Buster?

https://release.debian.org/buster/freeze_policy.html

Thanks,
Jeremy Bicha