Code review comment for lp:~sylvain-pineau/checkbox/fix-1227684

I'm open to a better API for this of course but so far the signal only set the job outcome to OUTCOME_UNDECIDED in such cases. The -temporary- job result that we get from running the job command with the Test button is not transmitted at all. I'm not for creating a new OUTCOME_UNDECIDED_PASS/FAIL that's why passing a second parameter seemed to be a good idea.