Compare circuit build timeouts to Torperf completion times

Our slow-ratio #1919 (moved) Torperf runs indicate that there could be a correlation between the Tor client's circuit build timeouts and Torperf's measured completion times. We should grep Tor's log for circuit build timeouts and combine them with Torperf's .data files. We could visualize the two data sets as scatter plot with CBTs on x and completion times on y.