Problem:
=======
Test Case 4 sporadically failed upon waiting for the slave to start during
master demotion to slave, due to a GTID event not existing in the new
master's binlog. If by chance the original slave (new master) did not yet
receive all the binlog events, then this failure could occur.

Solution:
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Sync slave with master GTID  before master demotion.

Reviewed By:
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Brandon Nesterenko <brandon.nesterenko@mariadb.com>