Update the subsuite report format

Only include results that are regressions, not all changes of expectation.
Start to refactor the code a little.
Use format like the subsuite format for the main report.

* List all regressions not just FAIL
* List all ERROR or CRITICAL level log messages
* Only generate HTML reports with some actual content
* Switch to python for generating all reports
* Refactor code so that LogManager object handles all the IO for creating the log zip
fixup! Use format like the subsuite format for the main report.
Merge pull request #138 from mozilla-b2g/jgraham/report_update

Update the subsuite report format