Fix sporadic failure of test case rpl.rpl_start_stop_slave

The test was expecting the I/O thread to be in a specific state, but thread
scheduling may cause it to not yet have reached that state. So just have a
loop that waits for the expected state to occur.
Signed-off-by: Kristian Nielsen <knielsen@knielsen-hq.org>

mysql-test/suite/rpl/t/rpl_start_stop_slave.test

@@ -19,7 +19,17 @@
 --source include/master-slave.inc
 
 connection slave;
---let $connection_id=`SELECT id FROM information_schema.processlist where state LIKE 'Waiting for master to send event'`
+--let $i= 100
+while ($i > 0) {
+  dec $i;
+  --let $connection_id=`SELECT id FROM information_schema.processlist where state LIKE 'Waiting for master to send event'`
+  if ($connection_id) {
+    let $i= 0;
+  }
+  if ($i > 0) {
+    --sleep 0.1
+  }
+}
 
 if(!$connection_id)
 {