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 and Resmoke prefixes to somewhat resembling JSON Log Output Format.

Resmoke prefixes can be transformed either into new fields/properties of the existing JSON log lines or into wrapper-objects for them.

The transformation can be done either by post-processing already available Resmoke output, or by modifying Resmoke source code. In the latter case, the fully-structured output should be activated (opted-in) with a separate parameter (feature flag, e.g., --structuredOutput = true) in order not to break possible upstream dependencies.