autopkgtest: avoid leaking stderr on deliberate failure

debian/patches/0006-testsuite-send-expected-stderr-to-stdout.patch

+From: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
+Date: Fri, 31 Aug 2018 09:26:38 -0400
+Subject: testsuite: send expected stderr to stdout
+
+---
+ testsuite | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/testsuite b/testsuite
+index 30f5fbe..bc15db4 100755
+--- a/testsuite
++++ b/testsuite
+@@ -65,7 +65,7 @@ trap cleanup EXIT
+ 
+ section "simple failing run"
+ # hddemux with no arguments and no listening file descriptors should fail:
+-if "$hddemux"; then
++if "$hddemux" 2>&1; then
+     false
+ fi
+ 

debian/patches/series

@@ -3,3 +3,4 @@
 0003-be-more-verbose-during-testsuite-termination.patch
 0004-avoid-emerg-8878-8878-mkdir-var-lib-nginx-body-faile.patch
 0005-testsuite-handle-other-nginx-temp_path-vars.patch
+0006-testsuite-send-expected-stderr-to-stdout.patch