Fix migration script for Masterfile.display_aspect_ratio

If there is no workflow to reference to find the display_aspect ratio, Mediainfo is ranon the absolute_location of a derivative instead.
If that fails, the user is warned that setting the display_aspect_ratio failed for that pid.
Set display_aspect_ratio to default of 4:3 if ratio can't be found.
Merge pull request #252 from avalonmediasystem/feature/VOV-2448

Fix migration script for Masterfile.display_aspect_ratio