Keyserver as a parameter

[459below]

Maybe it would make sense to misuse the keyfile field to pass the keyserver address to the keyscript.

The executable at the indicated path is executed with the key file from the third field of the crypttab as its only argument

[fetzerms]

This might be a good idea. On the other hand we're dependant on the actual handling of crypttab for systemd etc. We should check if this works properly first.