worker: append the run id to the start of each log

[josephjclark]

When looking at worker logs it can be hard to tell what run a log line refers too.

We should prefix each line coming out of the engine with the run id, so its clear. Maybe the engine should do this actually. Whatever.

Maybe we can use a short form of the id to make it more readable? just the first 6 digits? But I don't want to make assumptions about the id format particularly. Perhaps if it's a UUID we show the first 6, otherwise we show the whole thing