Add Nagios check for CollecTor
We currently have a metrics-specific Nagios host that we want to shut down soon. One of its checks is to see whether CollecTor's files are becoming unavailable or stale. This check is not easily transferable to Tor's Nagios host, because it depends on a code base that is not being maintained anymore and that we want to deploy on Tor's Nagios host. That's why I rewrote this check in a simple Python script to be deployed on Tor's Nagios instance.
anarcat and/or weasel: do you have any concerns about deploying this check in Tor's Nagios host alongside the Onionoo check?
irl: do you spot any checks in this Python script that are way off, or other checks that are missing?
atagar, other Python people: do you mind reviewing the Python code for general code improvements? The goal is to have a single, self-contained, easy-to-read Python script that produces just the data we need for Nagios to send out alerts.