listen to `docker stats` while container is executed

[mmaelicke]

To get some basic resource allocation by each container run, we should listen to the stream of docker stats, or call docker stats --no-stream periodically. In addition, the runtime of each tool should be monitored. If that works somehow, these logs should be added as metadata to the step tarball.

This will be a two-step issue:

• profile the run using docker stats and append the JSON output to the step container
• Implement a Reducer function, which is used to reduce stats logs to basic aggregated resource info