Ensure that views and templates are cleaned up.

This is being done currently in `ember-dev`, but since it is Ember specific we
should move it into the Ember test configuration directly.

Related:

https://github.com/emberjs/ember-dev/commit/600c5e6e0fd60903ad9cdc79839d338c7f994ec7 
https://github.com/emberjs/ember-dev/pull/95