Ths will allow automatic scan of known formats.
Errors are printed only if something is wrong with already detected metadata.
This change means that it is responsibility of the caller to print an error
message if needed.
Also fix some places without a message.
Fixes: #642
Currently the "add" action adds the token to all keyslots, this
changes the behaviour to make sure the token is added to the first
keyslot that can be unlocked using the provided passphrase.
Provides example of loadable token handler for activation
json validation and metadata dump.
For creating new ssh example token use special cryptsetup-ssh
binary.
