R1:e41a64607e68

Retain repository update cooldowns across daemon restarts

Summary:
Ref T11665. Fixes T7865. When we restart the daemons, the repository pull daemon currently resets the cooldowns on all of its pulls. This can generate a burst of initial load when restarting a lot of instance daemons (as in the Phacility cluster), described in T7865. This smooths things out so that recent pulls are considered, and any repositories which were waiting keep waiting.

Somewhat counterintuitively, hosted repositories write…