mattdrayer/api-progress-generator-fix: Repaired existence check

@martynjames @fredsmith -- here's an updated progress generator to run in the staging environment.  We may not want to take the current tip of master due to some recent changes to organizations which require some baking time in integration/QA.  So what we should do here is merge to master and then simply put a copy of generate_progress_entries.py on the staging server, then run it.
No, the problem was that we were overloading the contextual use of get_or_create -- it works as expected, but including the 'completions' value in the filter was causing the script to make a bad decision.