tests/sess.t: test #14: Change return value from 9 to 2

There's been some weird things about the return value from die(), but it
seems as 2 is correct. For some background, here is a log message from
utils.git:

  commit e7d00e10bcd5bd1edac781aaab3225d8d6f97b8c
  Author: Øyvind A. Holm <sunny@sunbase.org>
  Date:   2014-07-16 14:33:15 +0200

      tests/std.t: test #28: Change return value from 9 to 2

      This is some old weirdness described in commit c6a3a03, also known as
      99f62ca8-5676-11e0-aa82-b7a467e4e366 ("std.t: Set return value in a test
      to 9", 2011-03-25 01:23:36 +0100). As I wrote in that log message:

        std.t: Set return value in a test to 9

        The test "Create bash script, file already exists, don’t use --force"
        originally contained the exit value 1, but die() seems to return some
        odd value. 9 = EBADF (Bad file number), and that makes no sense. I’d
        expect it would return 17 (EEXIST, File exists), but apparently not.

        Oh well, let’s see if it’s consistent on various systems.

      It's changed now, I'll try to set it to 2 and see if it's the same
      everywhere.

      9a5163a0-0ce6-11e4-890b-c80aa9e67bbd

27ac33a2-0cf5-11e4-bdd6-c80aa9e67bbd