initramfs cryptroot hook script doesn't install cryptsetup if keyfile but no keyscript

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Instead of simply warning the user I've developed an alternative approach which does away with the problem entirely.

In this solution I alter the initramfs 'cryptroot' script to support unlock using the keyfile. Currently it will only do that if supported by a keyscript but the two are actually orthogonal.

If a keyscript is specified the keyfile will be available to it via the environment CRYPTTAB_KEY as usual.

The new feature:

If a keyfile is not specified $cryptkey will contain "-" (for /dev/stdin) and 'cryptsetup' will receive the output of the $cryptkeyscript 'askpass' executable's /dev/stdout as usual.

If a keyfile is specified without a keyscript 'cryptroot' will pass it to 'cryptsetup' via --key-file $cryptkey.

The code does not seem to exist anymore in cosmic and newer, so marking this an incomplete for those as I'm not sure if they are still affected and what happened there precisely.

Anyhow,bionic also seems to be affected looking at a key-file grep.

Doesn't affect post-bionic releases. Marking as fixed.