log-slave-updates and circul repl

This is a test case fix for BUG#13861.


mysql-test/r/rpl_dual_pos_advance.result:
  Fix for a test case for BUG#13861.
mysql-test/t/rpl_dual_pos_advance.test:
  Fix for a test case for BUG#13861.
  
  master_pos_wait() requires slave sql thread running. But it is not
  guaranteed for this test case. As we use start slave until it may
  execute all events and shutdown before master_pos_wait() is started.
  
  On the other hand it is safe just to wait for slave to stop here,
  as start slave returns _after_ sql thread is started.