randomtest fixes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/testsuite/du/du-works b/testsuite/du/du-works
index 46a336d..4db684a 100644
--- a/testsuite/du/du-works
+++ b/testsuite/du/du-works
@@ -1,3 +1,5 @@
+# FEATURE: CONFIG_FEATURE_DU_DEFAULT_BLOCKSIZE_1K
+
 d=/bin
 du "$d" > logfile.gnu
 busybox du "$d" > logfile.bb