[Dubbo-ci failed] fixed travis-ci failed because of test cases.

[zonghaishang]

What is the purpose of the change

fixed travis-ci failed because of test cases. see: com.alibaba.dubbo.rpc.protocol.thrift.AbstractTest

Brief changelog

dubbo-rpc-thrift/src/test/java/com/alibaba/dubbo/rpc/protocol/thrift/AbstractTest.java

-    static final int PORT = 30660;
+    protected int PORT = NetUtils.getAvailablePort();

+    TServerTransport serverTransport;
+
     protected void init() throws Exception {
-        TServerTransport serverTransport = new TServerSocket(PORT);
+
+        serverTransport = new TServerSocket(PORT);

+        try{
+            if(serverTransport != null){
+                // release port if used
+                serverTransport.close();
+            }
+        }catch (Exception e) {
+            // ignore
+        }

Verifying this change

should start ci test

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