http{s}: don't connect to localhost on invalid URL

If the URL passed to `http{s}.request` or `http{s}.get` is not properly
parsable by `url.parse`, we fall back to use `localhost` and port 80.
This creates confusing error messages like in this question
http://stackoverflow.com/q/32675907/1903116.

This patch throws an error message, if `url.parse` fails to parse the
URL properly.

Previous Discussion: #2966
PR-URL: #2967

Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_client.js

@@ -22,6 +22,9 @@ function ClientRequest(options, cb) {
 
   if (typeof options === 'string') {
     options = url.parse(options);
+    if (!options.hostname) {
+      throw new Error('Unable to determine the domain name');
+    }
   } else {
     options = util._extend({}, options);
   }

lib/https.js

@@ -163,6 +163,9 @@ exports.Agent = Agent;
 exports.request = function(options, cb) {
   if (typeof options === 'string') {
     options = url.parse(options);
+    if (!options.hostname) {
+      throw new Error('Unable to determine the domain name');
+    }
   } else {
     options = util._extend({}, options);
   }

test/parallel/test-http-invalid-urls.js

@@ -0,0 +1,19 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const http = require('http');
+const https = require('https');
+const error = 'Unable to determine the domain name';
+
+function test(host) {
+  ['get', 'request'].forEach((method) => {
+    [http, https].forEach((module) => {
+      assert.throws(() => module[method](host, () => {
+        throw new Error(`${module}.${method} should not connect to ${host}`);
+      }), error);
+    });
+  });
+}
+
+['www.nodejs.org', 'localhost', '127.0.0.1', 'http://:80/'].forEach(test);