Actually, my experience is the opposite. I personally know of two recent cases wherein the individual was cleared for work by clinics in their home countries, and when tested in Qatar, were found to have active TB. This means a positive chest x-ray, positive skin test, followed by positive sputum cultures. Qatar was willing to let them remain in country, and be treated, with continuing medical surveillance. It was the employees' company that arranged for each person's visa to be cancelled, and the individual to be deported.

I do think that if you are reading this, and you are not a medical professional, you should acquaint yourself futher with the TB disease process. Then you will better understand the significance of a 'tiny speck of scar tissue'.
I have many years of international healthcare experience. I find the health care in Qatar, as it is right now, to be sound. The physical facilities are undergoing improvement, but the medical judgement is already very good.
Yes, it is disappointing when something like this happens, but as adults, let's realize that:
1. Clinical tests performed in your home country can be wrong. This is why Qatar re-tests to begin with.
2. People buy, and submit, fake test results all the time.
3. The real point here people, is that if you are found to be positive for something, this is you chance, and maybe your ONLY chance, to do something about it. GO home if necessary, but get treated, and see that your family gets treated if need be. THEN worry about the job. Be thankful you were diagnosed definitively. For your family's sake, and for your own life.