Update edx-eng-dashboard for Jenkins cluster

This PR updates the dashboard to point to the new Jenkins instance (jenkins.testeng.edx.org).  For the most part, I just changed the URL and updated the code to handle HTTPS correctly.

The big changes are:

* It now parses the Cobertura coverage JSON instead of using coverage.py.  I've split the coverage numbers into "lms", "cms", "common lib," "common app", and "javascript"

* I deleted some example files that we aren't using on the dashboard.