updated builds4h analysis class

This branch adds builds4h attribute existence checks for log_url and slavename. It also stores a unique list of job_guids for every object analyzed, this facilitates generating accurate counts for total buildernames of a given type seen and how many times each buildername has missed an attribute or regular expression. In order to run this you will need to delete the existing `treeherder/webapp/media/builds4hanalysis/builds4h_analysis.json` and if you're actively running the task, you will need to restart the celery worker to execute the updated code.