nvie/rq — pull request #434 by jtushman (2014-10-09 18:15:35+00:00)
Title: triggering shutdown by setting a redis flag

[Preliminary PR -- do not merge]

**Problem Statement**
We use rq on heroku and there way the shutdown the worker that runs rq does not ensure a safe shutdown.

### HEROKU
https://devcenter.heroku.com/articles/dynos

When a worker is stoped by ps:scaling or pushing out a new release or any heroku operation.
The dyno manager sends the working SIGTERM

The process then has 10 seconds to shut down gracefully.

If the process is still alive -- then SIGKILL is then sent

So if a job takes more then 10 secs (which many of our jobs do) -- we are going to be out of luck.

So we needed a datastore approach. This PR is my first pass at that approach.