The test could fail with a duplicate key error because switching to non-GTID
mode could start at the wrong old-style position. The position could be
wrong when the previous GTID connect was stopped before receiving the fake
GTID list event which gives the old-style position corresponding to the GTID
connected position.

Work-around by injecting an extra event and syncing the slave before
switching to non-GTID mode.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>