Fix test cases to work with non-standard --vardir.

Rename mix_innodb_myisam_binlog-master.opt; when the test was moved to
separate stm/row test cases, the .opt were not moved along with it,
causing a 60-second test duration because of default lock timeout :-(

mysql-test/include/partition_layout.inc

@@ -9,5 +9,5 @@ eval SHOW CREATE TABLE t1;
 # listing of files belonging to the table t1
 if ($ls)
 {
-   --exec ls var/master-data/test/t1*
+   --exec ls $MYSQLTEST_VARDIR/master-data/test/t1*
 }