fixed issue alibaba#4813, support metric.port = -1 (alibaba#4891)

Author: coalchan

server/src/main/java/com/alibaba/otter/canal/server/embedded/CanalServerWithEmbedded.java

@@ -73,7 +73,7 @@ public void start() {
         if (!isStart()) {
             super.start();
             // 如果存在provider,则启动metrics service
-            if(metricsPort < 0) {
+            if(metricsPort > 0) {
                 loadCanalMetrics();
                 metrics.setServerPort(metricsPort);
                 metrics.initialize();