Add try-catch clauses around all update queues.

Now we will at least get an error message when an Exception occurs
instead of silently killing the thread.

src/main/java/net/floodlightcontroller/util/StackTraceUtil.java

+package net.floodlightcontroller.util;
+
+import java.io.PrintWriter;
+import java.io.StringWriter;
+
+/** 
+ * Utility class to get a stacktrace as a nice string
+ * 
+ * @author gregor
+ *
+ */
+
+public class StackTraceUtil {
+    public static String stackTraceToString(Throwable t) {
+        StringWriter sw = new StringWriter();
+        t.printStackTrace(new PrintWriter(sw));
+        return sw.toString();
+    }
+}