branches/5.1: innodb_bug51920.test: Make the test quicker and more deterministic.

Suggested by Vasil Dimov.

mysql-test/innodb_bug51920.result

@@ -9,10 +9,5 @@ SELECT ID FROM INFORMATION_SCHEMA.PROCESSLIST
 WHERE INFO="UPDATE bug51920 SET i=2"
 INTO @thread_id;
 KILL @thread_id;
-SELECT sleep(2);
-sleep(2)
-0
-SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID=@thread_id;
-ID	USER	HOST	DB	COMMAND	TIME	STATE	INFO
 ERROR 70100: Query execution was interrupted
 DROP TABLE bug51920;

mysql-test/innodb_bug51920.test

@@ -22,8 +22,9 @@ WHERE INFO="UPDATE bug51920 SET i=2"
 INTO @thread_id;
 
 KILL @thread_id;
-SELECT sleep(2);
-SELECT * FROM INFORMATION_SCHEMA.PROCESSLIST WHERE ID=@thread_id;
+let $wait_condition =
+  SELECT COUNT(*)=0 FROM information_schema.processlist WHERE ID=@thread_id;
+-- source include/wait_condition.inc
 
 connection con1;
 -- error ER_QUERY_INTERRUPTED