fix a couple of dbug tests not to write to /tmp

mysql-test/r/mdev6830.result

-drop table if exists t1,t2,t3;
-drop view if exists v2,v3;
+set @@debug_dbug= 'd,opt';
 CREATE TABLE t1 (pk INT PRIMARY KEY) ENGINE=MyISAM;
 CREATE TABLE t2 (
 f1 DATE,

mysql-test/r/select_debug.result

@@ -6,7 +6,7 @@ insert into t1 values (2,2), (1,1);
 create table t2 (a int);
 insert into t2 values (2), (3);
 set session join_cache_level=3;
-set @@debug_dbug= 'd:t:O,/tmp/trace.out';
+set @@debug_dbug= 'd,opt';
 explain select t1.b from t1,t2 where t1.b=t2.a;
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	2	Using where

mysql-test/t/mdev6830-master.opt

---debug

mysql-test/t/mdev6830.test

-
+#
+# MDEV-6830 Server crashes in best_access_path after a sequence of SELECTs invollving a temptable view
+#
 --source include/have_debug.inc
 
---disable_warnings
-drop table if exists t1,t2,t3;
-drop view if exists v2,v3;
---enable_warnings
+set @@debug_dbug= 'd,opt';
+
 CREATE TABLE t1 (pk INT PRIMARY KEY) ENGINE=MyISAM;
 
 CREATE TABLE t2 (

mysql-test/t/select_debug.test

@@ -10,7 +10,7 @@ create table t2 (a int);
 insert into t2 values (2), (3);
 
 set session join_cache_level=3;
-set @@debug_dbug= 'd:t:O,/tmp/trace.out';
+set @@debug_dbug= 'd,opt';
 
 explain select t1.b from t1,t2 where t1.b=t2.a;
 select t1.b from t1,t2 where t1.b=t2.a;