Make HTTP errors returned from the Aphlict server more specific

Summary: Ref T5651. Currently, the Aphlict server returns either `200 OKAY` or `400 Bad Request`. We could return more specific errors in some cases and this may assist with debugging.

Test Plan:
Sent myself a test notification at `/notification/status/` and saw the Aphlict server process the request (running in debug mode). Also poked around with `curl`:

```
> curl http://localhost:22281/
405 Method Not Allowed

> curl http://localhost:22281/ -d ""
400 Bad Request

> curl http://localhost:22281/foobar/
404 Not Found
```

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5651

Differential Revision: https://secure.phabricator.com/D9967

src/applications/notification/client/PhabricatorNotificationClient.php

@@ -40,6 +40,8 @@ final class PhabricatorNotificationClient {
 
   private static function postMessage(array $data) {
     $server_uri = PhabricatorEnv::getEnvConfig('notification.server-uri');
+    $server_uri = id(new PhutilURI($server_uri))
+      ->setPath('/');
 
     id(new HTTPSFuture($server_uri, json_encode($data)))
       ->setMethod('POST')

support/aphlict/server/aphlict_server.js

@@ -163,6 +163,7 @@ var start_time = new Date().getTime();
 
 var receive_server = http.createServer(function(request, response) {
   // Publishing a notification.
+  if (request.url == '/') {
     if (request.method == 'POST') {
       var body = '';
 
@@ -185,11 +186,16 @@ var receive_server = http.createServer(function(request, response) {
             request.socket.remoteAddress,
             err);
           response.statusCode = 400;
-        response.write('400 Bad Request');
+          response.write('400 Bad Request\n');
         } finally {
           response.end();
         }
       });
+    } else {
+      response.statusCode = 405;
+      response.write('405 Method Not Allowed\n');
+      response.end();
+    }
   } else if (request.url == '/status/') {
     request.on('data', function() {
       // We just ignore the request data, but newer versions of Node don't
@@ -212,8 +218,8 @@ var receive_server = http.createServer(function(request, response) {
       response.end();
     });
   } else {
-    response.statusCode = 400;
+    response.statusCode = 404;
-    response.write('400 Bad Request');
+    response.write('404 Not Found\n');
     response.end();
   }
 }).listen(config.admin, config.host);