I've been periodically using an actual logger inside
integration-tests to debug things, so I figured it would be actually
worthwhile to add actual logging support so you don't have to modify the
unit tests to produce output.
We now provide a logger to each of the RunnerProto and RecorderProto in
tests that prefixes the records with the process (runner, recorder) that
it would occur in.
Since `cargo test` runs unit tests in parallel, to get useful output you
need to use:
```
cargo test -p integration-tests -- --nocapture --test-threads 1
```
to force them to run sequentually. Otherwise, output from several tests
will be mixed together.