we should insert alert DB once , and trigger this type of alert 3 times (#1622)

dolphinscheduler-server/src/main/java/org/apache/dolphinscheduler/server/master/MasterServer.java

@@ -152,10 +152,8 @@ public class MasterServer implements IStoppable {
             @Override
             public void run() {
                 if (zkMasterClient.getActiveMasterNum() <= 1) {
-                    for (int i = 0; i < Constants.DOLPHINSCHEDULER_WARN_TIMES_FAILOVER; i++) {
-                        zkMasterClient.getAlertDao().sendServerStopedAlert(
-                                1, OSUtils.getHost(), "Master-Server");
-                    }
+                    zkMasterClient.getAlertDao().sendServerStopedAlert(
+                        1, OSUtils.getHost(), "Master-Server");
                 }
                 stop("shutdownhook");
             }

dolphinscheduler-server/src/main/java/org/apache/dolphinscheduler/server/worker/WorkerServer.java

@@ -177,9 +177,7 @@ public class WorkerServer implements IStoppable {
             public void run() {
                 // worker server exit alert
                 if (zkWorkerClient.getActiveMasterNum() <= 1) {
-                    for (int i = 0; i < Constants.DOLPHINSCHEDULER_WARN_TIMES_FAILOVER; i++) {
-                        alertDao.sendServerStopedAlert(1, OSUtils.getHost(), "Worker-Server");
-                    }
+                    alertDao.sendServerStopedAlert(1, OSUtils.getHost(), "Worker-Server");
                 }
                 stop("shutdownhook");
             }

dolphinscheduler-server/src/main/java/org/apache/dolphinscheduler/server/zk/ZKMasterClient.java

@@ -247,10 +247,8 @@ public class ZKMasterClient extends AbstractZKClient {
 	 */
 	private void alertServerDown(String serverHost, ZKNodeType zkNodeType) {
 
-	    String serverType = zkNodeType.toString();
-		for (int i = 0; i < Constants.DOLPHINSCHEDULER_WARN_TIMES_FAILOVER; i++) {
-			alertDao.sendServerStopedAlert(1, serverHost, serverType);
-		}
+		String serverType = zkNodeType.toString();
+		alertDao.sendServerStopedAlert(1, serverHost, serverType);
 	}
 
 	/**