give limited access to pg

test/src/test/java/cn/edu/tsinghua/iginx/integration/expansion/postgresql/PostgreSQLCapacityExpansionIT.java

@@ -23,6 +23,7 @@ public PostgreSQLCapacityExpansionIT() {
     Constant.expPort = dbConf.getDBCEPortMap().get(Constant.EXP_PORT_NAME);
     Constant.readOnlyPort = dbConf.getDBCEPortMap().get(Constant.READ_ONLY_PORT_NAME);
     wrongExtraParams.add("username:wrong, password:postgres");
+    // wrong password situation cannot be tested because trust mode is used
   }
 
   /** 执行一个简单查询1000次，测试是否会使连接池耗尽，来验证PG的dummy查询是否正确释放连接 */