Listener creation error is misleading

If a listener is created but it fails to listen on the configured port, the error is reported as:

MXB_ERROR("Listener '%s' was created but failed to start it.", name);

This is misleading as the listener is destroyed immediately after this. The error message should not mention the creation at all as starting it is a part of creating.

In addition, the listener configuration is persisted before the starting is attempted. This means that a potentially faulty configuration is persisted on disk.