The fde-setup-request command is used inside the fde-setup hook. It will
return information about what operation for full-disk encryption is
requested and auxiliary data to complete this operation.
The fde-setup hook should do what is requested and then call
"snapctl fde-setup-result" and pass the result data to stdin.
Here is an example for how the fde-setup hook is called initially:
$ snapctl fde-setup-request
{"op":"features"}
$ echo '{"features": []}' | snapctl fde-setup-result
Alternatively the hook could reply with:
$ echo '{"error":"hardware-unsupported"}' | snapctl fde-setup-result
And then it is called again with a request to do the initial key setup:
$ snapctl fde-setup-request
{"op":"initial-setup", "key": "key-to-seal"}
$ echo "{"sealed-key":"$base64_encoded_sealed_key"}" | snapctl fde-setup-result
