module unification: initializer test files are included for `ember serve`

Relates to #42. Mistakenly opened here: ember-cli/ember-cli-chai#37.

reproduction

1. clone the reproduction repo git clone --single-branch -b bug-initializer-test https://github.com/efx/poc-bug.git && cd poc-bug && npm install && bower install
2. run ember build or ember serve
3. Notice that the initalizer test files are being included when they shouldn't.

[rwjblue]

Seems like we need to allow excludes? 🤔

[rwjblue]

Closed by #53