job/validation:

For EB hazard, if `hazard_curves_from_gmfs` is true, `ground_motion_fields`
must also be true.
tests/job/validation_test:

Added `test_gmfs_false_hazard_curves_true` test case for event base hazard.
Merge pull request #1160 from larsbutler/haz-curve-gmf-validation

Event-Based Hazard: Better hazard curve / GMF validation

[r=matley] [f=1167302]