You need not worry.. come with a clear job offer in your hand and in many cases banks allow defaulters after seeing the current conditions and by submission of an undertaking to payback all dues within some stipulated time..

Even if you are blacklisted, your bank in Kuwait will be informed about your arrival.. then you can send proposal to settle the amount after joining the job at Qatar..

I m repeating, you must have clear appointment letter from the Qatar company..

Another option, if you have any friend in Kuwait, just tell him now to contact that bank of Kuwait and inform bank that you will settle the outstanding balance within 6 month or so....

All the best !!