supervising/supervisor:

Don't check for failed nodes when OQ_NO_DISTRIBUTE is enabled. Otherwise,
this can cause spurious errors and failures in the supervisor.
supervising/supervisor:

Added a comment explaining why the failed node checked is skipped in certain
cases.
Fixed a test calling an incorrect function
validate_site_model bug fix, enabling a previously disabled qa test
Merge pull request #1006 from gem/1099801

Fix PickleFieldTestCase.test_get_prep_value
updated test_validate_site_model to consider a degenerate case
Merge pull request #1007 from larsbutler/superv-support-for-no-distribute

Supervisor support for `no_distribute`

[r=matley]
Merge branch 'master' of https://github.com/gem/oq-engine into site_model_validation_bug_fix
Added config file for 3 new qa tests
removed old comment and unused import
Added the skeleton for the scenario_damage calculator
Added an exposure_model.xml
Refactoring, rename of a constant, added a comment
Relaxed constraint db side, kept and update validation rule in validation.py
Added comment to clarify site model convex hull area expansion
export/hazard:

Use `iterator()` when fetching (potentially) large hazard curves, to avoid
caching them. This drastically reduces spikes in memory usage for the export.
export/hazard:

Slightly faster and slightly leaner (less memory usage) query for hazard
curve export.
export/hazard:

Updated HazardCurveData query to avoid returning and constructing millions of
Point geometry objects.
export/hazard:

When exporting hazard curves, order DB query results by `id`. This ensures
that results have a stable and consistent order.
replaced because with if :)