Should route all queries to master in serializable isolation level

This is not only affect correctness but also affect replication:

In serializable isolation level , if a user thread is reading some record for a long time, and the sql thread want to apply binlog which would update the same record, then sql thread will be blocked by S lock util timeout, then the replication will be paused;

Although we should advice user not use serializable iso level in rwsplit service, but when they do we should avoid interrupting replication too;