The appointment of John Cryan as chief executive of Deutsche Bank sent shares in Germany’s largest lender up 8 percent on Monday as investors judged the Briton a more credible contender than his two ousted predecessors to revive its fortunes. Cryan faces one of the most difficult jobs in global finance as he aims to move Deutsche Bank beyond the raft of regulatory and legal probes that have bedeviled the bank under its current management and execute a strategic overhaul.