Refine the using of setting read-only

We now abuse the system read-only, which is a dangerous operation.

Even worse, when system is set to read-only, I could not find why we set it to read-only, there is no related log.

 

We only set read-only when losing data continuously, otherwise, we must store more data as we can.

 

(1) Add a parameter to let user choose how to handle error in IO: shutdown or set readonly.

(2) Change readOnly field to an enum class SystemStatus, which contains NORMAL and READONLY, and open a SQL for the user to query.

(3) In the IoTDBConfig.setReadOnly() function, if it receive a true, we need to log the stack trace with the information "change system mode to read-only". To avoid missing the log outside.

if (readOnly)

{ logger.error("change system mode to read-only", new RuntimeException()); }

(4) Check all places that set read-only, this is a dangerous operation in the deployment environment, and we should avoid using this if not necessary.