Removed warnings when celery is not installed
Removed warnings when celery is not installed


Former-commit-id: 3217137d6b4566ebffaab0f10d144746139e8e64 [formerly dcda73c5751ca2ff65029b1e026971f33c77ceca] [formerly dcda73c5751ca2ff65029b1e026971f33c77ceca [formerly f2b21422d66ab12aeb0e5e55786c406756669166]]
Former-commit-id: 01737effea74fb7a07e955f44015e5e7c3b90fb8
Former-commit-id: eb4bc0749cf1eeb831a0fa08aad59f50fafdcd45
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine