By Parisa Hafezi and Angus McDowall DUBAI, July 9 (Reuters) - Iran buries its slain Supreme Leader Ayatollah Ali Khamenei on Thursday at the country's holiest shrine, with his son and successor Mojtaba Khamenei still hidden from public view after being disfigured in the strike that killed his father. The burial in Mashhad in northeast Iran follows a week of mass funeral processions, rallies and mourning ceremonies that has coincided with a renewed burst of conflict with the United States followi