Add dry_run option to save_report. Also clean up some more "option={}" cases

When I was developing the DoD scraper, I found it very useful to add this option to the save_report function. Basically a "dry run" (--dry_run=True) means that you download all the metadata for a report, and even save it as report.json, but don't actually donwload the PDF. This makes it possible to scrape a large number of reports quickly and verify that they pass through the validation.

Of course, this change requires that all of the scrapers call save_report() with options=options. If you think this is a good idea, I can add that in a later CL.