Test results should be immutable if not in-progress

[MartinKolarik]

I've run into a weird case where a test was marked as a timeout, but a second later, the timeout message was overwritten with the results. Setting aside the fact that the probe shouldn't have taken 32 seconds to report the results, the API should still prevent this as it is confusing and contradicts our documentation.

We already have a check here, but when a test is marked as a timeout, we don't seem to increment probesAwaiting. Additionally, there's no check when calling recordProgress(), I think we should use a lua script with a check there as well.