Steps to reproduce:
1. Add a workflow which includes mkv / matroska as intermediate format
2. Inspect mediapackage
mkv files have mime type "undefined"
MediaInspector logs error, e.g.
2014-12-03 16:14:04 ERROR (MediaInspector:155) - Unable to find mimetype for /data/matterhorn/work/shared/workspace/collection/composer/40298477.mkv
mimetype should be "video/x-matroska"
Workaround (if any):