On selfdestruct, first destroy all active keyslots through the
cryptsetup library, before zeroing the luks header.

Also take a factor two safety margin when zeroing the luks header,
and halt the machine (instead of rebooting) after selfdestruct.

Replace the very similar encryption_keys_post and encryption_keys_put
callback functions by a single handler function, with a boolean flag to
separate the two variants.

basic PUT and DELETE behavior, still does some weird stuff with random unicode characters appearing some times

Sleep for a bit after we received a signal to stop cryptops-api. This
gives the request handler that asked to stop the server more time to
send its response to the client, fixing a race condition.

Extend the `encryption/add` command to repartition the encrypted container,
copy the authorized_keys file to the configuration partition, generate a new
ssh host key for the dropbear running in the initrd, and reboot after it's
done.