Subtask for #1329

The daemon might log "run successfully" but the job failed. Or log a "write error" or "incomplete" but the job succeeds.
It should print out the outcome (same on the dashboard) explicitly.

How to reproduce

testground run single --plan=example --testcase=output --builder=docker:go --runner=local:docker --instances=1 --wait

In the log you will see "job finished successfully", the command exists with code = 0,
but if you open the dashboard (localhost:8042) or check the extended status, its actual outcome is "failed".