This check loads Django, and as such must be run as the zulip user.
Repeat the same pattern used elsewhere in nagios, of writing a state
file, which is read by `check_cron_file`.
An organization with at most 5 users that is behind on payments isn't
worth spending time on investigating the situation.
For larger organizations, we likely want somewhat different logic that
at least does not void invoices.
Alex Vandiver
Vishnu KS
Tim Abbott