Improve logging

[samuel-jimenez]

Distributed compilation has been failing silently for me for some time. It now fails loudly, but the process of troubleshooting lead to some extremely spammy output.

I think the logging could use the following improvements:

1. Split out heartbeat logging
2. Add extra warnings in build server on compilation failure

Thoughts?

[Xuanwo]

Looks good to me. PRs are welcome.