Silence mknod "failure" in the test-suite setup

We're only testing whether mknod is usable or not, so a failure is not a
failure, just information. Silence the distracting message.

tests/atlocal.in

@@ -64,7 +64,7 @@ if grep -q '#define WITH_CAP 1' "${abs_top_builddir}/config.h"; then
 else
     CAP_DISABLED=true;
 fi
-if mknod foodev c 123 123; then
+if mknod foodev c 123 123 2>/dev/null; then
    MKNOD_DISABLED=false
    rm -f foodev
 else