Add loop summary to in-progress logging for latency test

[timpokorny]

Each of the tests print status about their progress each 1/10th of the total loops.

The throughput test currently prints a loop summary, with information about what has happened since the last time summary information was printed. Below is an example:

INFO [main] wantest: Finished loop 3000 -- 3832ms, 39720 events received (10365/s), 10.12MB/s

Add similar support to the latency test, which currently just printed "Completed loop X"

[timpokorny]

Suspect will close as Won't Fix. A bit much work to generate the stats for this each time for relatively little gain?