Check for existing rebuilds for a legislature

[chrismytton]

In a similar spirit to everypolitician/countries_json_updater#5 when we receive a request to rebuild a legislature we should check if there's already a rebuild queued for that legislature. If there is then we don't need to queue the rebuild again.

[tmtmtmtm]

This seems like fairly low-hanging fruit as part of speeding the rebuilder up (by reducing some rebuilds to zero!)

Other than a little bit of refactoring we should do to remove the duplication of doing this in two places, is this largely just a matter of replacing the perform_async calls with something that checks RebuilderJob.jobs first to see if there's already something with the same arguments?

[chrismytton]

Other than a little bit of refactoring we should do to remove the duplication of doing this in two places, is this largely just a matter of replacing the perform_async calls with something that checks RebuilderJob.jobs first to see if there's already something with the same arguments?

Yep, that's pretty much it. I'll add this to my stack, should hopefully be fairly straightforward!

[chrismytton]

Pull request for this is here #54 but need to revisit it and fix the tests so that they actually fail when expected.