gsup_test: also check stderr

Configure logging to be deterministic and add stderr checking to testuite.at.

However, exclude the thousands of message modification log lines from the log
to not have a huge test expectation file.

Change-Id: I0dd7112967a64a168556b62e5ec15107b7608ffb
diff --git a/tests/testsuite.at b/tests/testsuite.at
index d6181c9..a3be0e7 100644
--- a/tests/testsuite.at
+++ b/tests/testsuite.at
@@ -212,7 +212,8 @@
 AT_SETUP([gsup])
 AT_KEYWORDS([gsup])
 cat $abs_srcdir/gsup/gsup_test.ok > expout
-AT_CHECK([$abs_top_builddir/tests/gsup/gsup_test], [0], [expout], [ignore])
+cat $abs_srcdir/gsup/gsup_test.err > experr
+AT_CHECK([$abs_top_builddir/tests/gsup/gsup_test], [0], [expout], [experr])
 AT_CLEANUP
 
 AT_SETUP([fsm])