Wrap migration in a transaction

[dboskovic]

The migration may or or may not error, as it has values like $userTable that are not guaranteed to be provided.

[dboskovic]

Still is a good idea to do this even if the issue causing the migration error is solved in #639

[andrewelkins]

Thanks

[oldFuryBird]

1. The transaction for manually using of laravel must control over rollbacks and commit.

    DB::beginTransaction();
    try{
  //...
    DB::commit();
    }catch(Exception $e){
  //...
   DB::rollBack();
  }
// or 
 if(condition)DB::commit();
 else DB::rollBack();

2. Mysql DDL action such as 'create,drop,delete table' will cause an implicit commit.It means
   DDL sql do not commit a transaction.See mysql-dev-refman