Avoid thousands of download progress log entries

They were filling up most of the build logs for Qt Creator at least.
Also print which file the progress info belongs to, since multiple
downloads are done simultaneously.

Change-Id: Ia1f42761f6eeeff41cfeed52e8ac2c63610400fb
Reviewed-by: Iikka Eklund <iikka.eklund@digia.com>