randomtest fixes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/testsuite/du/du-works b/testsuite/du/du-works
index 4db684a..e320f1d 100644
--- a/testsuite/du/du-works
+++ b/testsuite/du/du-works
@@ -3,4 +3,6 @@
 d=/bin
 du "$d" > logfile.gnu
 busybox du "$d" > logfile.bb
-cmp logfile.gnu logfile.bb
+cmp logfile.gnu logfile.bb && exit 0
+diff -u logfile.gnu logfile.bb
+exit 1