Relays can upload a new descriptor every 2 minutes
Two relays started publishing descriptors every 2 minutes, and this caused issues for Metrics-lib: https://lists.torproject.org/pipermail/metrics-team/2018-February/000661.html
Maybe it's a crashing bug in 0.3.3.1-alpha?
In any case, we should probably restrict relays to a few (~6?) descriptors per
hour consensus interval, and enforce this limit using the state file.