Toshiba Chairman Satoshi Tsunakawa will become chief executive, the company said in a statement. : TOKYO (Reuters) -Toshiba Corp CEO Nobuaki Kurumatani resigned on Wednesday amid controversy over a $20 billion buyout bid from CVC Capital Partners and the conglomerate's shares surged on reports that more suitors were planning offers. The statement gave no reason for the resignation but Kurumatani has come under much fire over the bid from CVC, his former employer, and his testy relations with the company's large activist shareholder base.