Changed main_query_cache_merge to use flush global status

mysql-test/main/query_cache_merge.result

@@ -3,7 +3,7 @@ set @save_query_cache_type=@@global.query_cache_type;
 SET GLOBAL query_cache_type=ON;
 SET LOCAL query_cache_type=ON;
 SET @@global.query_cache_size=1355776;
-flush status;
+flush global status;
 select count(*) from t00;
 count(*)
 514

mysql-test/main/query_cache_merge.test

@@ -18,7 +18,7 @@ SET @@global.query_cache_size=1355776;
 # more then 255 (257) merged tables test
 #
 
-flush status;
+flush global status;
 disable_query_log;
 --disable_warnings
 let $1 = 257;