Post-push fixes: I forgot to include the new files
start_slave.inc and stop_slave.inc in the previuos push.
mysql-test/include/start_slave.inc:
Added file.
Purpose: start slave synchronously, waiting for the two
threads to start.
mysql-test/include/stop_slave.inc:
Added file.
Purpose: stop slave synchronously, waiting for the two
threads to stop.
