Fixed the XML export of gmf_scenario and added a schema-consistency check in the tests
Merged from master
Restored the accidentally removed check_export functionality in export/hazard_test.py
Fixed the export of UHS files
Merge branch 'master' of github.com:gem/oq-engine into 1167324
Merge pull request #1132 from gem/1167324

Make sure the generated XML are valid according to NRML