The test case rpl_do_grant fails sporadically on PB2 with "Access
denied for user 'create_rout_db'@'localhost' ...". Inspecting the
test case, one may find that if issues a GRANT on the master
connection and immediately after it creates two new connections
(one to the master and one to the slave) using the credentials
set with the GRANT.
      
Unfortunately, there is no synchronization between master and
slave after the grant and before the connections are
established. This can result in slave not having executed the
GRANT by the time the connection is attempted.
      
This patch fixes this by deploying a sync_slave_with_master
between the grant and the connections attempt.