Fix cost calculation in test_if_cheaper_ordering() to be cost based

The original code was mostly rule based and preferred clustered or
covering indexed independent of cost.

There where a few test changes:
- Some test changed from using filesort to index or table scan. This
  happened when most of the rows had to be sorted and the ORDER BY could
  use covering or a clustered index (innodb_mysql, create_spatial_index).
- Some test changed range to filesort. This where mainly because the range
  was scanning most of the rows or using index scan + row lookup and
  filesort with table scan is cheaper. (order_by).
- Change in join_cache was because sorting 2 rows is faster than retrieving
  10 rows.
- In selectivity_innodb.test one test changed to use a cheaper index.

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

@@ -1407,13 +1407,13 @@ EXPLAIN SELECT * FROM t2 WHERE b=1 ORDER BY a;
 id	1
 select_type	SIMPLE
 table	t2
-type	ref
+type	index
 possible_keys	bkey
-key	bkey
-key_len	5
-ref	const
+key	PRIMARY
+key_len	4
+ref	NULL
 rows	16
-Extra	Using where; Using index; Using filesort
+Extra	Using where
 SELECT * FROM t2 WHERE b=1 ORDER BY a;
 a	b	c
 1	1	1