Clean up startup logs in `docker run` quickstart command

Created by: sqs

This commit quiets the following log messages when running cmd/server:

21:41:56  postgres_exporter | time="2019-12-08T21:41:56Z" level=info msg="Established new database connection to \"127.0.0.1:5432\"." source="postgres_exporter.go:814"
21:41:56    zoekt-webserver | 2019/12/08 21:41:56 listening on 127.0.0.1:3070
21:41:57  postgres_exporter | time="2019-12-08T21:41:57Z" level=info msg="Established new database connection to \"127.0.0.1:5432\"." source="postgres_exporter.go:814"
21:41:57  postgres_exporter | time="2019-12-08T21:41:57Z" level=info msg="Semantic Version Changed on \"127.0.0.1:5432\": 0.0.0 -> 11.6.0" source="postgres_exporter.go:1335"
21:41:57  postgres_exporter | time="2019-12-08T21:41:57Z" level=info msg="Starting Server: :9187" source="postgres_exporter.go:1576"
21:41:58 management-console | t=2019-12-08T21:41:58+0000 lvl=info msg="management-console: listening" addr=:2633
21:41:58 management-console | 2019/12/08 21:41:58 Generating and using self-signed TLS cert/key

It also makes the management-console log message more easily readable.

Having clean log output for the docker run quickstart command is important to create a good first impression. Of course, we don't want to suppress any logs that are helpful, but I don't think any of the ones removed in this PR are actually helpful enough to merit being shown to all users at the default log level.