Web: ignore superfeedr subscribe failures

it's pretty unreliable right now 😕

for #550

tests/test_web.py

@@ -536,6 +536,19 @@ def test_get_or_create_subscribes_superfeedr(self, mock_get, mock_post):
         }, auth=ANY)
         self.assertEqual(NOW, self.user.key.get().superfeedr_subscribed)
 
+    def test_get_or_create_subscribe_error(self, mock_get, mock_post):
+        self.user.obj.mf2 = ACTOR_MF2_REL_FEED_URL
+        self.user.obj.put()
+        self.user.has_redirects = False
+        self.user.put()
+
+        mock_post.return_value = requests_response('Nope', status=500)
+
+        user = Web.get_or_create('user.com')
+        self.assert_entities_equal(user, self.user, ignore=['updated'])
+        self.assertIsNone(user.superfeedr_subscribed)
+        self.assertIsNone(user.superfeedr_subscribed_feed)
+
     def test_get_or_create_existing_subscribed(self, *_):
         self.user.superfeedr_subscribed = NOW
         self.user.put()
@@ -748,8 +761,7 @@ def test_target_fetch_has_no_content_type(self, mock_get, mock_post):
             no_content_type,  # https://user.com/ webmention discovery
             no_content_type,  # http://not/fediverse webmention discovery
         )
-        got = self.post('/queue/webmention',
-                               data={'source': 'https://user.com/reply'})
+        got = self.post('/queue/webmention', data={'source': 'https://user.com/reply'})
         self.assertEqual(204, got.status_code)
         mock_post.assert_not_called()
 

web.py

@@ -641,7 +641,11 @@ def maybe_superfeedr_subscribe(user):
         'format': 'atom',
         'retrieve': 'true',
     })
-    resp.raise_for_status()
+    try:
+        resp.raise_for_status()
+    except BaseException as e:
+        util.interpret_http_exception(e)
+        return
 
     user.superfeedr_subscribed = util.now()
     user.superfeedr_subscribed_feed = url