mandos-ctl: Refactor

* mandos-ctl (commands_and_clients_from_options): Take options as an
                                                  argument.  Move
                                                  parser setup into
                                                  new function and
                                                  move extra parse
                                                  checking into main.
  (add_command_line_options): New.
  (main): Create parser here and call add_command_line_options() to
          add options to it.