tests: fix cleanup

The cleanup routine cleared the variable holding the temp dir name
before it was deleted, so it wasn't deleted.

This commit first deletes the temp folder, and clears the variable
afterwards.

Signed-off-by: Gyorgy Sarvari <skandigraun@gmail.com>

Author: OldManYellsAtCloud

tests/run

@@ -2,8 +2,8 @@
 d=
 cleanup() {
         if [ -n "$d" ]; then
-                d=
                 rm -rf "$d"
+                d=
         fi
 }
 trap cleanup EXIT