Restored a needed celery import
Restored a needed celery import


Former-commit-id: 1106c109caf4b0cb9a8413e0dee672207c4d6d32 [formerly c18cbf6de62062663bc511a3203a7907387cae6a]
Former-commit-id: fdc2cdb9ebb9d9af19547f954cf45b6a4e3bcb5f
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine