Restart job workers after X runs to prevent memory leaks

[njam]

Goal: restart job worker processes once in a while to avoid filling up memory. Like apache (or php-fpm) we could just exit a job worker after X job runs. The CLI manager would then restart the worker.

Default: 1000

Implemented in #2414
Released: 2016-11-22
Log: https://cargomedia.loggly.com/search#terms=%22Respawning%20dead%20child.%22
Keeping for tracking.

cc @tomaszdurka @alexispeter

[njam]

Works great!
Check out the memory usage since November 11th:

cc @cargomedia/devops