Change the way the overall throughput messages/sec is calculated

[timpokorny]

Summary

The value for the overall throughput in messages/second is a bit coarse at the moment. It has a strange habit of being exactly the same in two separate federates that make up a run. I suspect this is because I'm just dividing the overall message count by the run time in seconds (rounded). To take this little inaccuracy away, the total runtime in millis should be used. That'll be slightly different for each federate and thus produce those ever so slightly more accurate (and believable) numbers.

INFO  [main] wantest:      ---------------------------------------------
INFO  [main] wantest:   All| 400000 |   26.1MB/s |  390.6MB |  28571/s |
INFO  [main] wantest:      ---------------------------------------------

Acceptance Criteria

Once complete:

• Generate messages/second by using run time in millis, not whole seconds