Require that "(exit $fail); exit $fail" be last line of each test.

Require that "(exit $fail); exit $fail" be last line of each test.

* maint.mk (sc_require_test_exit_idiom): New rule to enforce policy.
* tests/cp/acl: Adhere to the new policy.
* tests/cp/preserve-gid: Likewise.
* tests/dd/misc:
* tests/install/create-leading:
* tests/ln/sf-1:
* tests/ls/symlink-slash:
* tests/misc/help-version:
* tests/misc/ls-time:
* tests/misc/nice:
* tests/misc/shred-remove:
* tests/misc/stty:
* tests/misc/stty-row-col:
* tests/mkdir/p-1:
* tests/mkdir/p-2:
* tests/mkdir/p-3:
* tests/mkdir/p-v:
* tests/mkdir/special-1:
* tests/mkdir/writable-under-readonly:
* tests/mv/acl:
* tests/mv/backup-is-src:
* tests/mv/diag:
* tests/mv/dir-file:
* tests/mv/force:
* tests/mv/hard-link-1:
* tests/mv/i-2:
* tests/mv/i-4:
* tests/mv/into-self:
* tests/mv/into-self-2:
* tests/mv/into-self-3:
* tests/mv/partition-perm:
* tests/mv/to-symlink:
* tests/rmdir/ignore:
* tests/tail-2/assert:
* tests/tail-2/assert-2:
* tests/touch/dangling-symlink:
* tests/touch/dir-1:
* tests/touch/empty-file:
* tests/touch/fifo:
* tests/touch/no-rights: Likewise.

Signed-off-by: Jim Meyering <meyering@redhat.com>