BERLIN (Reuters) -Two big investors in Aareal Bank on Wednesday rejected a sweetened $2.1 billion bid for the German lender, with one calling it “lousy” and a second saying it significantly undervalued the group. The buyout group, which includes U.S.-based Advent International and Centerbridge Partners, earlier on Wednesday raised their offer to 31 euros per share from 29 euros, hoping to convince investors who had been unhappy with the price. They said the new bid, which values the lender at 1.86 billion euros ($2.10 billion), was final. In a statement Adam Epstein, co-founder of Teleios, whi…