* luks_device: allow passphrases to contain newlines
This is useful when passing binary keyfiles from an ansible vault, as
it removes the restriction that the binary data cannot contain newlines.
The only exception is adding a new key to an existing container, as in
that case the two passphrases are separated by a new line.
* add integration tests and a changelog fragment
* attempt to also make luks_add_key work with passphrases containing
newlines
* use a deterministic method to generate keyfile 3, improve changelog
formatting
* add licence and copyright to keyfile3.txt to satisfy CI
