Buffet server: upgraded cherrpy to 3.2, use @tools.json_out to return json properly.

Cherrypy provides good tooling for auto-converting dictionaries to json and
setting the return header correctly. Let's use it!

TEST=Unittests + curl and expected return types.

Change-Id: I1ab95a3f4cc606313c7412e2c582c3b9ea873469
Reviewed-on: https://chromium-review.googlesource.com/195332
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
8 files changed