Buildbot runbook

Our buildbot instance has a habit of breaking due to excess load. 
 Restarting the worker 
 If the worker (primary, handling nix evaluations) explodes, it can be restarted. 
 ssh root@buildbot.lix.systems 'systemctl restart buildbot-worker.service' 
 Re-trying spurious CI failures 
 Those with the relevant permissions can click the "rebuild" button on a given CI job, but in order to count for Gerrit's checks and set the Verified +1 flag, you must restart the top-level lix/nix-eval job ; restarting e.g. a single test or build will not affect things on the Gerrit side.