By Andrew MacAskill and Muvija M LONDON (Reuters) -Boris Johnson returned to Britain from holiday on Saturday to consider an audacious bid for a second term as prime minister in a race that could pit him against his former finance minister whose resignation in July helped drive him out of office. Potential candidates to replace Prime Minister Liz Truss, who quit on Thursday after six weeks in office, were embarking on a frantic weekend of lobbying to secure enough nominations to enter the leadership contest before Monday’s deadline. Johnson, who was on holiday in the Caribbean when Truss resig…