use table_prefix from database config when creating migrations table

When migrations table is created, it uses table name from migration.php config file.
If we have table_prefix in database config (it is used by Database module to create full table names when preforming queries) it affects queries preformed in tasks-migrations module also, but the migrations table was created without prefix, so the table doesn't exists error is thrown. 
The migrations table needs to be created also with the prefix.