Finish Refactoring View Tests for HTMLBars

https://github.com/emberjs/ember.js/pull/9769#discussion_r21162519

Standardize and Replace calls to `append` and `destroy` with helpers
wrapped in `run` calls.
Merge pull request #9773 from seanpdoyle/htmlbars-test-cleanup

Finish Refactoring View Tests for HTMLBars
Ensure {{unbound if}} works for undefined values.