[DOP-20962] import original celery & modify it for tests

tests/test_integration/celery_test.py

@@ -1,18 +1,3 @@
-from celery import Celery
+from syncmaster.worker.config import celery
 
-from syncmaster.settings import Settings
-from syncmaster.worker.base import WorkerTask
-
-# TODO: remove settings object creating during import
-settings = Settings()
-
-celery = Celery(
-    __name__,
-    broker=settings.broker.url,
-    backend="db+" + settings.database.sync_url,
-    task_cls=WorkerTask,
-    imports=[
-        "syncmaster.worker.transfer",
-        "tests.test_integration.test_scheduler.test_task",
-    ],
-)
+celery.conf.update(imports=list(celery.conf.imports) + ["tests.test_integration.test_scheduler.test_task"])