Merge pull request #1544 from gem/remove-tests

Removed EventBasedHazardCalculatorTestCase
Simplified the risk preparation phase
Small simplification
A trick to partition the ruptures by trt_id
Merge branch 'master' of github.com:gem/oq-engine into better-risk
Added a meaningful comment
Fixed a bug with the quantile_hazard_curves attribute
Merge branch 'fix-quantile' into better-risk
Used get_risk_models from commonlib
Changed the scenario calculators to use directly the workflow API
Merged from better_risk