Attempt at fixing p4-trellis STC scenario

the mininet stdout was clogged with stratum log affecting test result

Change-Id: I0f138d3c32bea14ec175fdc745bda58ac74d1bbc
diff --git a/tools/dev/mininet/bmv2.py b/tools/dev/mininet/bmv2.py
index d079482..f99aeaf 100644
--- a/tools/dev/mininet/bmv2.py
+++ b/tools/dev/mininet/bmv2.py
@@ -367,7 +367,9 @@
             '-cpu_port=%s' % self.cpuPort,
             '-external_hercules_urls=0.0.0.0:%d' % self.grpcPort,
             '-local_hercules_url=localhost:%d' % self.grpcPortInternal,
-            '-max_num_controllers_per_node=10'
+            '-max_num_controllers_per_node=10',
+            '-logtosyslog=false',
+            '-logtostderr=true'
         ]
         return " ".join(args)