max_slave_connections=0 may create slave connections after a switchover

Configuring readwritesplit in the follwing way can cause a slave connection to be created if the first command after a master switchover is a read.

[ReadWriteSplit]

type=service

router=readwritesplit

max_slave_connections=0

master_failure_mode=fail_on_write

master_reconnection=true

The server will be used for reads until a write arrives at which point it will be discarded. The expected behavior would be that the first read selects the master server if no slave connections should be created.

In the case of a failover, the read will fail as the old master server is no longer valid and the logic for routing reads does not currently allow a new master connection to be created (MXS-5086).