Container Support

A sample progess report for docker:

 progress_reports:
  - message: Downloading tag list
    state: completed
    total: 1
    done: 1
  - message: Downloading Artifacts
    state: running
    done: 415
  - message: Associating Content
    state: running
    done: 641
  - message: Processing Tags
    state: completed
    total: 135
    done: 135

While the task is running, the total value for tasks: Downloading Artifacts and Associating Content is not present. These values are populated once the tasks are completed.