Add use_syslog to Marconi config

This patch adds use_syslog option to the marconi config file. This
is needed to allow marconi to run, when USE_SCREEN is set to False
in devstack.

Change-Id: I547697ec2745975e235a4e58cde81132ac37b70d
diff --git a/lib/marconi b/lib/marconi
index 8cfc55c..29ae386 100644
--- a/lib/marconi
+++ b/lib/marconi
@@ -95,6 +95,7 @@
     sudo chown $USER $MARCONI_API_LOG_DIR
 
     iniset $MARCONI_CONF DEFAULT verbose True
+    iniset $MARCONI_CONF DEFAULT use_syslog $SYSLOG
     iniset $MARCONI_CONF 'drivers:transport:wsgi' bind $MARCONI_SERVICE_HOST
 
     iniset $MARCONI_CONF keystone_authtoken auth_protocol http