Factor out common code for starting a Mongod process into methods
Use distinct labels for the tokumx and mongodb output
Rename #getStarter() to #newStarter() to make the purpose of the method clearer

Suggested-by: @benmccann
Rename #get{RuntimeConfig,RuntimeConfigBuilder} to #new{RuntimeConfig,RuntimeConfigBuilder} as well
Merge pull request #434 from Collaborne/river-test-mongod-logging

Use distinct labels for the tokumx and mongodb outputs