always fails

Test seems to run 'test_stripe' at $dir directory, but $dir is never
set. If $dir is adjusted to $PWD, the test still fails with:

    mdadm: /dev/loop2 is not suitable for this array.
    mdadm: create aborted
    ++ return 1
    ++ cmp -s -n 8192 /dev/md0 /tmp/RandFile
    ++ echo cmp failed
    cmp failed
    ++ exit 2