do not print error log into log_error.log file when the server receives a wrong SQL

Hi, 

log_error.log and log_warn.log are two important files for DBA, and the messages in those files should be valuable enough. 

Now, if a client sends a incorrect sql to iotdb, e.g., " show select a from from root.b;", then the server will print error info to log_error.log, like :

2019-11-23 10:35:13,749 [pool-2-IoTDB-JDBC-Client-thread-15] ERROR org.apache.iotdb.db.service.TSServiceImpl:653 - meet error while parsing SQL to physical plan:2019-11-23 10:35:13,749 [pool-2-IoTDB-JDBC-Client-thread-15] ERROR org.apache.iotdb.db.service.TSServiceImpl:653 - meet error while parsing SQL to physical plan:org.apache.iotdb.db.exception.query.IllegalASTFormatException: Parsing error, statement [show devices root.perform.group_9] failed when parsing AST tree to generate logical operator. Detailed information: [line 1:5  'show'] at org.apache.iotdb.db.qp.QueryProcessor.parseSQLToAST(QueryProcessor.java:102) at org.apache.iotdb.db.qp.QueryProcessor.parseSQLToPhysicalPlan(QueryProcessor.java:69) at org.apache.iotdb.db.service.TSServiceImpl.executeStatement(TSServiceImpl.java:633) at org.apache.iotdb.service.rpc.thrift.TSIService$Processor$executeStatement.getResult(TSIService.java:1465) at org.apache.iotdb.service.rpc.thrift.TSIService$Processor$executeStatement.getResult(TSIService.java:1450) at org.apache.thrift.ProcessFunction.process(ProcessFunction.java:39) at org.apache.thrift.TBaseProcessor.process(TBaseProcessor.java:39) at org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:286) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748)

This kind of error can just be considered as an info level log, and do not need to print its exception stack.