Update ember-cli-test-loader & fix load ordering.

Previously, the modules were required before our test-helper was loaded.
This causes errors in ember-qunit (as it expects the resolver to be
set).

Also, ember-cli-test-loader fixed an issue that caused all modules to be
required once one was.
Merge pull request #881 from rjackson/update-ember-cli-test-loader

Update ember-cli-test-loader & fix load ordering.