interference between server.close and worker.disconnect

[Offirmo]

According to node documentation, calling worker.disconnect() will close existing servers. And that's true (tested it) Calling worker.disconnect()will even throw an uncaught if the servers are already closed (tested it also).

So the shutdown routine must be rewritten so that if in a worker, the midleware should only call worker.disconnect() and not close the server directly.

PR pending.

[Offirmo]

Note : my fork https://github.com/Offirmo/domain-middleware has this issue solved.