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: https://github.com/nodejs/node/pull/2966
PR-URL: https://github.com/nodejs/node/pull/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/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);
   }