Moved the expected outputs of the ScenarioDamage QA tests in qa_tests_data

And changed the export routines to make use of the new DamageWriter class. The pull request https://github.com/gem/oq-risklib/pull/93 is needed. The tests are running here: https://ci.openquake.org/job/zdevel_oq-engine/895
This is a preliminary step for https://bugs.launchpad.net/oq-engine/+bug/1389260