Stabilize and clean up a test

The counter buffer_flush_background_total_pages may be unreliable,
because pages can be flushed in different means.
So, let us only check INNODB_BUFFER_POOL_PAGES_FLUSHED.

mysql-test/suite/innodb/r/purge_secondary.result

@@ -141,18 +141,9 @@ WHERE NAME='test/t1';
 OTHER_INDEX_SIZE
 1
 ALTER TABLE t1 DROP INDEX `sidx`;
-INSERT INTO t1 () VALUES (),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),();
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT * FROM seq_1_to_544;
 ALTER TABLE t1 FORCE, ALGORITHM=INPLACE;
 ALTER TABLE t1 FORCE, ALGORITHM=INPLACE;
-SELECT NAME, SUBSYSTEM FROM INFORMATION_SCHEMA.INNODB_METRICS
-WHERE NAME="buffer_LRU_batch_flush_total_pages" AND COUNT > 0;
-NAME	SUBSYSTEM
-buffer_LRU_batch_flush_total_pages	buffer
 SELECT (variable_value > 0) FROM information_schema.global_status
 WHERE LOWER(variable_name) LIKE 'INNODB_BUFFER_POOL_PAGES_FLUSHED';
 (variable_value > 0)

mysql-test/suite/innodb/t/purge_secondary.test

 --source include/have_innodb.inc
+--source include/have_sequence.inc
 
 # Ensure that the history list length will actually be decremented by purge.
 SET @saved_frequency = @@GLOBAL.innodb_purge_rseg_truncate_frequency;
@@ -123,18 +124,10 @@ WHERE NAME='test/t1';
 # Work around MDEV-13942, Dropping the spatial index to avoid the possible hang
 ALTER TABLE t1 DROP INDEX `sidx`;
 
-INSERT INTO t1 () VALUES (),(),(),(),(),(),(),(),(),(),(),(),(),(),(),(),();
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
-INSERT INTO t1 (a) SELECT NULL FROM t1;
+INSERT INTO t1 (a) SELECT * FROM seq_1_to_544;
 ALTER TABLE t1 FORCE, ALGORITHM=INPLACE;
 ALTER TABLE t1 FORCE, ALGORITHM=INPLACE;
 
-SELECT NAME, SUBSYSTEM FROM INFORMATION_SCHEMA.INNODB_METRICS
-WHERE NAME="buffer_LRU_batch_flush_total_pages" AND COUNT > 0;
-
 SELECT (variable_value > 0) FROM information_schema.global_status
 WHERE LOWER(variable_name) LIKE 'INNODB_BUFFER_POOL_PAGES_FLUSHED';