Provide an ability to have Resmoke logs in a fully-structured (JSON) format.

By default, resmoke merges its own output with the output of all spawned processes. While MongoDB server process outputs are in valid JSON, Resmoke output is in 'plain text'. In addition, Resmoke prepends all other lines with process-related information, which is also not in JSON and may break the existing JSON format.

For this task we need to modify Resmoke own output to somewhat resembling JSON Log Output Format.

Resmoke prefixes for MongoDB server process output are handled in SERVER-97964.

The fully-structured output should be activated (opted-in) with a separate parameter (see SERVER-97956) in order not to break possible upstream dependencies.