mock router should always on the top of the router chain

Author: lexburner

dubbo-cluster/src/main/java/org/apache/dubbo/rpc/cluster/router/mock/MockInvokersSelector.java

@@ -34,7 +34,7 @@
 public class MockInvokersSelector extends AbstractRouter {
 
     public static final String NAME = "MOCK_ROUTER";
-    private static final int MOCK_INVOKERS_DEFAULT_PRIORITY = Integer.MAX_VALUE;
+    private static final int MOCK_INVOKERS_DEFAULT_PRIORITY = Integer.MIN_VALUE;
 
     public MockInvokersSelector() {
         this.priority = MOCK_INVOKERS_DEFAULT_PRIORITY;