qa_tests/_utils:

Added base QA test class method for testing with variable precision.
qa_tests/hazard/event_based/case_2:

Added event based QA test, case 2.
qa_tests/hazard/event_based/case_4:

Adapted case 4 for the event-based calculator.
qa_tests/hazard/event_based/case_8:

Initial draft of case_8 for the event-based calculator.
qa_tests/hazard/event_based:

Fixed imports.
qa_tests/hazard/event_based/case_8:

Removed case 8; I couldn't get it to converge with the expected results in a
reasonable run time.
qa_tests/hazard/event_based:

Updated the GSIM references in cases 2 and 4.
qa_tests/hazard/event_based:

Corrected source model names in cases 2 and 4; they were copied from the
classical cases.
qa_tests/hazard/event_based:

Added `hazard` nose attr to cases 2 and 4.
qa_tests/hazard/event_based/case_6:

Implemented case 6, based on classical hazard case 6.
qa_tests/hazard/event_based/case_6:

Removed case 6. Couldn't get results to converge in a reasonable run time.
Merge pull request #1086 from larsbutler/eb-qa-var-precision

More event-based hazard QA tests

[r=matley] [f=1088864]