add missing import in celeryconfig.py
add missing import in celeryconfig.py


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Former-commit-id: 91871f88032686efe78113d805f49d937e896786
Former-commit-id: d29ff9a2a6fbed028ef9be763aa6ebfc96da674b
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine