Because of the way per-command arguments are handled, this is a little
different from the way e.g. kitchen handles it: any inspec command can
take the flag `--diagnose` to have it dump configuration first.
This add support for a JSON configuration file, where both
inspec detect --json-config=config.json
and
inspec detect --json-config=- <config.json
allow for reading the JSON config. There is no validation of its keys
in place.