test: fix broken FreeBSD test

Fixes net-server-max-connections-close-makes-more-available
Handles connection 'error' event so the test ends.

PR-URL: #1881
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Brendan Ashworth <brendan.ashworth@me.com>

test/parallel/test-net-server-max-connections-close-makes-more-available.js

@@ -28,6 +28,11 @@ var createConnection = function(index) {
       sent.push(msg);
     });
 
+    connection.on('error', function(err) {
+      assert.equal(err.code, 'ECONNRESET');
+      resolve();
+    });
+
     connection.on('data', function(e) {
       console.error('connection ' + index + ' received response');
       resolve();