Code review comment for ubuntu-security-tools:json-output

Thanks @eslerm - however I would really like to avoid having to duplicate the arguments between cmd and cmd_json - hence my suggestion for a single boolean above. If we have these duplicated then it will only be a matter of time before they start to diverge - so better to have a single source of truth and then a way to make this do json IMO.

If that can't work, how about a `json_flags` argument or similar which would be a list of command-line options to use to have the tool output json instead - and then you could update the existing shellcheck.sh to look for these and DTRT so we don't have to have two shellcheck wrapper scripts as well.

Thoughts?