process_contributors consuming memory every hour until OOM

[MoralCode]

Our instance was within 10 GB of its 124 GB memory capacity (and thats after adding 8G swap space) and still experiencing processes being killed due to the kernel OOM killer. htop revealed that the processes using the most memory were all core task workers (with a couple of facade ones thrown in).

This could probably use some additional investigation to see if the fix could be similar to what we have seen before in facade.

I also think setting a high memory limit per task and maybe slowly lowering it to something reasonable could also assist with keeping augur resource usage within predictable margins.

[MoralCode]

mem usage seems to be deteriorating on an hourly basis post-collection-reset

[MoralCode]

Flower shows that collect_contributors is taking up all of the core task slots. Presumably spawning a new one each hour.

Confirmed by a htop run from within the augur container, showing matching PIDs