Improve readability of logs

[cbgbt]

Issue or Feature Request:
The logs in Brupop are currently emitted using Bunyan-formatted messages. These are machine-parseable, but they actually end up being pretty difficult for humans to read when checking Brupop logs in kubernetes.

Let's replace this with a plaintext log format that retains useful context but is easier for a human to quickly grok.

[cbgbt]

To instrument this, we can replace the bunyan formatter in our tracing configurations with something else. A similar formatting configuration is enabled in each of the agent, apiserver, and controller.