Log the queries received by the Whisper finder

Log information about the queries received by the Whisper finder:

- startTime
- endTime
- rangeInMins
- pattern

For example:

```
{"start": 1400162254, "rangeInMins": 60, "end": 1400165854, "pattern": "*.agents.*.metricsReceived", "event": "find_nodes"}
```