Fix sys_vars innodb_empty_free_list_algorithm_basic

Post xtradb 5.6.36 merge the output has changed.

mysql-test/suite/sys_vars/r/innodb_empty_free_list_algorithm_basic.result

 SET @start_value = @@GLOBAL.innodb_empty_free_list_algorithm;
 SELECT @@GLOBAL.innodb_empty_free_list_algorithm;
 @@GLOBAL.innodb_empty_free_list_algorithm
-backoff
+legacy
 SELECT @@SESSION.innodb_empty_free_list_algorithm;
 ERROR HY000: Variable 'innodb_empty_free_list_algorithm' is a GLOBAL variable
 SET GLOBAL innodb_empty_free_list_algorithm='legacy';