By Paul Sandle, Elizabeth Piper and Andrew MacAskill LONDON (Reuters) -Rishi Sunak looked set to become Britain’s next prime minister after Boris Johnson withdrew from the contest on Sunday, saying that although he had enough support to make the final ballot he realised the country and the Conservative Party needed unity. Johnson had raced home from a holiday in the Caribbean to try and secure the backing of 100 lawmakers to enter Monday’s contest to replace Liz Truss, the woman who succeeded him in September after he was forced to quit over a string of scandals. He said he had secured the bac…