avoid running duplicated IotDB server/node

Backgroud: 

1) Sometimes, customers wrongly run 2 IoTDB servers porcess from same directory at same time, which can cause Tsfiles' damage.

2)  Another JIRA:  https://issues.apache.org/jira/browse/IOTDB-3306 has done some change.  IOTDB-3306's code change let rpc-server starting as early as possible, so that the second IoTDB server proccess can detect listening port conflict before changing Tsfile and then exit.

3) But  IOTDB-3306's fix will let IoTDB server open rpc service too early, which can casue some client task failure.

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After discussion with HouHaoNan, we think there is better solution than IOTDB-3306's fix.  New solution is to change start-server.sh to detect whether 1 IoTDB server porcess from same directory has existed.