Aug 23 (Reuters) - Britain's FTSE 100 index is seen opening down 7 points on Wednesday, according to financial bookmakers. * BHP: Global miner BHP Billiton on Wednesday unveiled a board shakeup that will see controversial director Grant King step down six months after joining the company amid concerns among investors over oil investments. * VODAFONE: Vodafone is in talks with BT's network subsidiary Openreach about a joint investment in ultrafast UK broadband, The Telegraph repo