test: merge environment, don't overwrite

The CI system requires that some environment variables are set so merge
our variables into the current environment instead of blindly replacing
it.

This will probably have to be repeated for other tests. C'est la vie.

test/simple/test-http-server-stale-close.js

@@ -22,6 +22,7 @@
 var common = require('../common');
 var assert = require('assert');
 var http = require('http');
+var util = require('util');
 var fork = require('child_process').fork;
 
 if (process.env.NODE_TEST_FORK) {
@@ -45,7 +46,7 @@ else {
   });
   server.listen(common.PORT, function() {
     fork(__filename, {
-      env: {NODE_TEST_FORK: '1'}
+      env: util._extend(process.env, {NODE_TEST_FORK: '1'})
     });
   });
 }