refactored P6TestPerformance to P6TestOutage; removed log msg history from P6LogQuery; fixes #15

please note I've removed log msg history (last log msg as well as last stacktrace) from the P6LogQuery.

As far as I've seen it was used for the tests purposes only. Anyway if someone needs it, can just provide custom implementation of P6Logger. (see introduced P6TestLogger).
I think purpose of P6spy is to proxy and log/detect outage/... but not to keep the last msg by default.

Sounds, like ready to merge to you guys?