2. Slice of fix for Bug#42003 tests missing the disconnect of connections <> default

- If missing: add "disconnect <session>"
   - If physical disconnect of non "default" sessions is not finished
     at test end: add routine which waits till this happened
+ additional improvements
  - remove superfluous files created by the test
  - replace error numbers by error names
  - remove trailing spaces, replace tabs by spaces
  - unify writing of bugs within comments
  - correct comments
  - minor changes of formatting
Fixed tests:
  backup
  check
  compress
  grant
  information_schema
  multi_update
  overflow
  packet
  query_cache_not_embedded
  sp-threads
  subselect
  synchronization
  timezone_grant

mysql-test/r/multi_update.result

@@ -375,7 +375,7 @@ update t2, t1 set t2.field=t1.field
 where t1.id1=t2.id2 and 0=1;
 delete t1, t2 from t2 inner join t1 on t1.id1=t2.id2
 where 0=1;
-delete t1, t2 from t2,t1 
+delete t1, t2 from t2,t1
 where t1.id1=t2.id2 and 0=1;
 drop table t1,t2;
 CREATE TABLE t1 ( a int );
@@ -443,12 +443,12 @@ delete t1 from t1,t2 where t1.col1 < (select max(col1) from t1) and t1.col1 = t2
 ERROR HY000: You can't specify target table 't1' for update in FROM clause
 drop table t1,t2;
 create table t1 (
-aclid bigint not null primary key, 
-status tinyint(1) not null 
+aclid bigint not null primary key,
+status tinyint(1) not null
 ) engine = innodb;
 create table t2 (
-refid bigint not null primary key, 
-aclid bigint, index idx_acl(aclid) 
+refid bigint not null primary key,
+aclid bigint, index idx_acl(aclid)
 ) engine = innodb;
 insert into t2 values(1,null);
 delete t2, t1 from t2 left join t1 on (t2.aclid=t1.aclid) where t2.refid='1';