Suppressing GUI server stack trace when running multiple STCs at the same time.

Change-Id: I4b40aa2017f8b2ee540380b8d4f94bd186ae73f7
diff --git a/utils/stc/src/main/java/org/onlab/stc/Main.java b/utils/stc/src/main/java/org/onlab/stc/Main.java
index ca04a7c..016c7cf 100644
--- a/utils/stc/src/main/java/org/onlab/stc/Main.java
+++ b/utils/stc/src/main/java/org/onlab/stc/Main.java
@@ -149,7 +149,7 @@
         try {
             server.start();
         } catch (Exception e) {
-            e.printStackTrace();
+            print("GUI already active; running without...");
         }
     }