By Tina Bellon and Joseph White (Reuters) -Automakers racing to develop battery-powered, software-driven vehicles to compete with Tesla Inc are confronting a new challenge: what technology to build themselves, and what to keep buying from suppliers. Becoming more vertically integrated by doing more manufacturing in-house represents a major shift for most global automakers, who have relied for decades on suppliers to produce critical parts and software, and manage sprawling manufacturing networks in low-wage countries. But some established automakers are embracing drastic changes to their longs…