Add new doctrine processors

Another useful thing here would be to handle the case of timed out connections before processing the message:

```php
    foreach ($this->connections as $connection) {
        if (!$connection->isConnected()) {
            continue; // Keep the connection lazy if not connection yet
        }

        try {
            $connection->query($connection->getDatabasePlatform()->getDummySelectSQL());
        } catch (DBALException $e) {
            $connection->close(); // close timed out connections so that using them connects again
        }
    }
```

An alternative to the try/catch is available in Doctrine DBAL 2.5 (currently in RC mode), allowing to have a better implementation in the mysqli driver as it is able to try reconnecting an existing connection (other drivers are just using the same try/catch)

```
if (!$connection->ping()) {
    $connection->close();
}
```

However, I don't think using this new version is worse it yet, given that the difference is only for the mysqli driver, and it is not yet stable.