MDEV-20523: rpl.create_or_replace_mix, rpl.create_or_replace_statement failed in buildbot with wrong result

Wait for the disconnect of the other connection to complete, before running
SHOW BINLOG EVENTS. Otherwise the DROP TEMPORARY TABLE that is binlogged
during disconnect may not have appeared yet depending on thread scheduling.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>