Bug#37312: Make test binlog_{row,stm}_innodb_stat more robust

The size of the Innodb_buffer_pool_pages differs by one byte on row versus statement
log, so neuter the last position of the stringified decimal representation.  Innobase
says the size isn't very important in any case.

Also, split out the "mixed" format to its own file, as mtr seems to dislike having only 
stm and row but not mix.

mysql-test/extra/binlog_tests/innodb_stat.test

@@ -41,6 +41,7 @@ drop table t1;
 
 # Test for testable InnoDB status variables. This test
 # uses previous ones(pages_created, rows_deleted, ...).
+-- replace_regex /51[12]/51_/
 show status like "Innodb_buffer_pool_pages_total";
 show status like "Innodb_page_size";
 show status like "Innodb_rows_deleted";