Write javelin2 logs to stderr

We currently don't keep the oslo-logging based javelin2 logs in gate
runs, making it very hard to debug. Fix that by logging to stderr.

There is a bug in oslo that is causing stdout to not work, so use
stderr.

Specify config file via CLI (added in
I1e82e0a8e72117ba55048b2dab7aa9a8ba00c1cb)

Change-Id: Idbdac27392121e348ae0ab93477c98a904f8c001
Co-Authored-By: Sean Dague <sean@dague.net>
Merge "Write javelin2 logs to stderr"