Instead of the current master rejoining to the diverged master, the
current master should remain as the master server. This behavior should be
explained by the extra GTID event injected by the failover process.
The test uses standard setup (1xMaster, 3xSlaves).
1. Shutdown master (server 1), check that autofailover promotes
a new master.
2. Stop MaxScale.
3. Start server 1 and add some events to it so it can no longer rejoin
cluster.
4. Start MaxScale, check that server 1 does not join.
5. Set current master to replicate from server 1, turning it to a relay
master.
6. Check that server 1 is master, all others are slaves (due to auto-rejoin).
