Test tool should average the latency data from tests

[chschrae]

Please provide us with the following information:

This issue is for a: (mark with an x)

- [ ] bug report -> please search issues before submitting
- [x ] feature request
- [ ] documentation issue or request
- [ ] regression (a behavior that used to work and stopped in a new release)

When running the voice assistant test tool, we output a summary that gives dialog count, dialogPassCount, and dialogPassRate. We should also output an average of the latency so users could get an idea of that.