DefaultPackager: Fix addon preprocessing
DefaultPackager: Fix addon preprocessing

`preprocessTree('test', ...)` assumes that the input tree has the tests in an `<app-name>/tests` folder, but the default packager implementation regressed and passed the tests in an non-nested `tests` folder. This commit fixes the packager to correctly pass the tests in `<app-name>/tests` again, by moving the `callAddonsPreprocessTreeHook()` call below the `Funnel` that does the `<app-name>` prefixing.

mike-north/ember-cli,elwayman02/ember-cli,buschtoens/ember-cli,kategengler/ember-cli,HeroicEric/ember-cli,Turbo87/ember-cli,fpauser/ember-cli,asakusuma/ember-cli,Turbo87/ember-cli,Turbo87/ember-cli,jgwhite/ember-cli,thoov/ember-cli,thoov/ember-cli,elwayman02/ember-cli,jgwhite/ember-cli,kategengler/ember-cli,thoov/ember-cli,Turbo87/ember-cli,ember-cli/ember-cli,buschtoens/ember-cli,fpauser/ember-cli,asakusuma/ember-cli,jgwhite/ember-cli,HeroicEric/ember-cli,raycohen/ember-cli,mike-north/ember-cli,HeroicEric/ember-cli,raycohen/ember-cli,ember-cli/ember-cli,balinterdi/ember-cli,jrjohnson/ember-cli,ember-cli/ember-cli,thoov/ember-cli,balinterdi/ember-cli,fpauser/ember-cli,mike-north/ember-cli,mike-north/ember-cli,fpauser/ember-cli,jgwhite/ember-cli,HeroicEric/ember-cli,jrjohnson/ember-cli