pipeline output to terminal

[nsheff]

we should think about how to capture terminal output from the pipeline, when calling looper.Run from caravel. Right now this output would be discarded, which is not a problem normally, but if you're running on localhost for example, you might want to be directly viewing the output in a test scenario.

perhaps we can just capture terminal output and show it, similar to how we will stream the log output from looper.... but it wouldn't be as simple as just having a stream handler; we'd need some kind of terminal capture.