By Parisa Hafezi and Angus McDowall DUBAI, July 10 - The whereabouts of Mojtaba Khamenei have been a mystery to Iranians and the rest of the world alike since his appointment as supreme leader a week after the strike that killed his father at the end of February. His absence from the main funeral ceremonies for former leader Ayatollah Ali Khamenei was so complete there was not even a written message, leaving people to guess at his plans for Iran at a turbulent time in the Islamic Republic's 47-y