* Update StudentModulePerCourseTask to use multipart upload.

* Move extra_modules calls into launcher's attach call: add boto,
  cjson, and filechunkio to argparse.

* Fix bug in PathSetTask.generate_file_list() with redundant root in
  returned path.

Change-Id: I8861ccfb02ee10c5188e11c9ceb86eca9f7b3363