WIP: Report aggregated results

[kakkoyun]

This PR attempts to aggregate round-trip (write and read) results and exit accordingly.

name=up caller=level.go:63 ts=2020-01-15T23:53:55.615866Z level=info caller=main.go:415 component=writer msg="number of requests" success=20 errors=0
name=up caller=level.go:63 ts=2020-01-15T23:53:55.615942Z level=info caller=main.go:415 component=reader msg="number of requests" success=19 errors=0
name=up caller=level.go:63 ts=2020-01-15T23:53:55.615966Z level=info caller=main.go:427 msg="total number of requests" success=39 errors=0
name=up caller=level.go:63 ts=2020-01-15T23:53:55.615991Z level=error caller=main.go:265 msg="run group exited with error" err="periodic request stopped: context canceled"
name=up caller=level.go:63 ts=2020-01-15T23:53:55.616031Z level=info caller=main.go:268 msg="up completed its mission!"

TODO

• Consider syncronizing requests, xref: Synchronize consecutive write/read request and reporting #5
• Introduce custom errors for actors
• Add tests

[kakkoyun]

It's a bit stale now. Closing it, I'm happy to work on it again when needed.