export/hazard:
export/hazard:

Made the `export_type` arg of `export` optional, defaulting to 'xml'.
This is so we cause so much disruption to users of this function,
namely QA test code.


Former-commit-id: 19a8fa4a1eb1fefd590d298567c6d9ea8b2c5cb0
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine