test: fix simple/net-pipe-connect-errors

When trying to connect to something that is not a UNIX socket, Linux returns
ECONNREFUSED, not ENOTSOCK.

We cannot atomically determine if the other end is a) a stale socket, or b) not
a socket at all, so let's accept both error codes.

test/simple/test-net-pipe-connect-errors.js

@@ -39,7 +39,7 @@ var notSocketClient = net.createConnection(
 );
 
 notSocketClient.on('error', function (err) {
-  assert.equal(err.code, 'ENOTSOCK');
+  assert(err.code === 'ENOTSOCK' || err.code === 'ECONNREFUSED');
   notSocketErrorFired = true;
 });