Fix most defaultPrevented test failures (#2172)
Use position in FindEnumStringIndex.

This is a shorter and probably slightly more efficient to write the loop.
auto merge of #2175 : Manishearth/servo/domtests-createevent, r=Ms2ger

#2172

All subtests of `dom/events/Event-defaultPrevented.html` pass now.

CustomEvent has yet to be implemented.(#2173)
Rename Event::default_prevented -> Event::canceled to better match spec (#2177)
Propagate the result of wptrunner.run_tests out of run.py.

This ensures that unexpected results cause 'make check-wpt' to fail.
auto merge of #2179 : Manishearth/servo/refactor-canceled, r=Ms2ger



See #2177
Update test expectations for #2172.
Update the expectations for Document-createEvent.html.
auto merge of #2178 : Ms2ger/servo/enum-position, r=jdm

This is a shorter and probably slightly more efficient to write the loop.
auto merge of #2180 : Ms2ger/servo/wpt-result, r=jdm

This ensures that unexpected results cause 'make check-wpt' to fail.
Remove not-yet-implemented methods from CharacterData.

This speeds up a web-platform-tests run by about 45 seconds (of 11-12 minutes)
by avoiding three timeouts.
auto merge of #2181 : Ms2ger/servo/update-expectation, r=jdm
auto merge of #2184 : Ms2ger/servo/remove-nyi-characterdata, r=jdm

This speeds up a web-platform-tests run by about 45 seconds (of 11-12 minutes)
by avoiding three timeouts.