Confusion between Jib and Skaffold output

We've had a number of situations now where users have encountered hard-to-diagnose authentication errors when using Jib with Skaffold. Often the image build succeeds with Jib but then Skaffold exits with a failure. For example, this [StackOverflow question](https://stackoverflow.com/questions/61213312/skaffold-dev-works-with-minikube-only-other-on-prem-cluster-fails?noredirect=1#comment108306145_61213312) has in the logs:

```
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 20.058 s
[INFO] Finished at: 2020-04-15T08:45:57+03:00
[INFO] ------------------------------------------------------------------------
Pruning images...
FATA[0024] exiting dev mode because first build failed: build failed: building [registry.demo/springtokube]: build artifact: getting image: GET http://registry.demo/v2/: : Not Found
```

We should make a clearer difference between builder output and Skaffold's output. Perhaps prefixing builder output with `> ` or `| `? Or clear _begin_ and _end_ markers.

And this error message doesn't indicate why it's trying to get the image.