(#7160) Support 'json' as a rendering method for CLI faces.

We already had some specialized support for rendering JSON using the PSON
libraries; this just extends that to recognize the request on the command line
for json to be identical to a request for pson.

Theoretically we should also support the format in our network rendering code,
but that is a much bigger change, in established code, that has more chance of
destabilizing the whole release.

Reviewed-By: Max Martin <max@puppetlabs.com>