export/hazard:
export/hazard:

Refactored metadata handling in hazard curv and hazard curve multi
exporters.


Former-commit-id: aa6e597165a468d4f00c8d563c4e00a9c3e2bdf4
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine