Improve client job reporting

Make client job reporting better by separating report data from presentation. Typically one does that by using a template engine, and that's what we've done.

The template engine used is json-template (https://code.google.com/p/json-template), and for that purpose, the python implementation is being shipped within the client library, given that the autotest client has to be mostly self-contained, and not count with a lot of 3rd party python libraries.

As a result, report generation is cleaner, and paves the road for things like generating HTML email job reports.