JOHANNESBURG, Aug. 27 (Xinhua)-- An improving supply chain could help South African wine industry and raise the country's economic competitiveness, according to a study released on Tuesday.   Lack of supply chain awareness is hampering the competitiveness of South Africa's wine industry, said the study released in Johannesburg.   "Many cellars are still thinking like fruit farmers who merely sell their produce to exporters. It's a mindset that can, and must urgently change,...