Munin chart idea: Failures in last X minutes

[mvl22]

Occasionally a route could fail for whatever reason, e.g. caused by some kind of timeout.

It would be useful therefore to have a Munin chart that scans the Apache logs for failures (5xx) in the last 5 minutes.

Presumably this could reuse this log file reader.
https://github.com/cyclestreets/cyclestreets-setup/blob/master/utility/readLogFile.py