fix bug NoneType object has no attribute push (#2403)

* fix bug NoneType object has no attribute push

the bug was raised by Celery and succeeded the bug ParsedInstance DoesNotExist. The ParsedInstance was being read immediately after being created which means it was not guranteed to be available in the replica. The fix aplied is to read the created ParsedInstance from the master database

* remove whitespace

* remove trailing whitespace

* fix formatting error

* do not run webhook signal as cellery task

also revert previous changes

* remove unnecessary quotes

* fix failing test

* read instance from master db when running signl

onadata/apps/restservice/signals.py

@@ -4,8 +4,11 @@
 """
 import django.dispatch
 from django.conf import settings
+from multidb.pinning import use_master
 
 from onadata.apps.restservice.tasks import call_service_async
+from onadata.apps.restservice.utils import call_service
+from onadata.apps.logger.models.instance import Instance
 
 ASYNC_POST_SUBMISSION_PROCESSING_ENABLED = getattr(
     settings, "ASYNC_POST_SUBMISSION_PROCESSING_ENABLED", False
@@ -23,7 +26,15 @@ def call_webhooks(sender, **kwargs):  # pylint: disable=unused-argument
     if ASYNC_POST_SUBMISSION_PROCESSING_ENABLED:
         call_service_async.apply_async(args=[instance_id], countdown=1)
     else:
-        call_service_async(instance_id)
+        with use_master:
+            try:
+                instance = Instance.objects.get(pk=instance_id)
+            except Instance.DoesNotExist:
+                # if the instance has already been removed we do not send it to the
+                # service
+                pass
+            else:
+                call_service(instance)
 
 
 trigger_webhook.connect(call_webhooks, dispatch_uid="call_webhooks")