SELECT INTO OUTFILE is routed to all servers

All queries that have a INTO OUTFILE component are routed to all servers. This is a somewhat questionable routing decision as the query actively modifies the file system on the slave server.

A more reasonable approach would be to treat the query as if it was modifying the database itself (in a way it does) and route it to the master. This would mirror the routing behavior that LOAD DATA INFILE has.