verbose Jaeger logs should be redirected to file

Created by: slimsag

Grafana and Prometheus both have their verbose logs redirected to a file (in both dev and sourcegraph/server deployments), so as to not pollute our application logs. Jaeger should follow the same pattern.

• Prometheus: https://sourcegraph.com/search?q=repo:%5Egithub%5C.com/sourcegraph/sourcegraph%24+prometheus.log&patternType=literal
• Grafana: https://sourcegraph.com/search?q=repo:%5Egithub%5C.com/sourcegraph/sourcegraph%24+grafana.log&patternType=literal

This should be fixed before we cut the release.