Add a debugging facility to the main runner script, and include debug messages at key points

Change-Id: Ieef53eafffee27089d30e2d21545868db7af6f64
Reviewed-on: https://review.openstack.org/31304
Reviewed-by: Monty Taylor <mordred@inaugust.com>
Approved: Sean Dague <sean@dague.net>
Reviewed-by: Sean Dague <sean@dague.net>
Tested-by: Jenkins