Fixes classNameBindings regression

`classNameBindings` was initialized as an empty array inside `propertiesFromHTMLOptions`
so we could maintain the same shape of the object via this
[PR](https://github.com/emberjs/ember.js/pull/5559).

When the view is [created](https://github.com/emberjs/ember.js/blob/master/packages/ember-views/lib/views/states/in_buffer.js#L38), `options.classNameBindings` is an empty array
and the view gets confused about its classes.

Scumbag @twokul.

Fixes #5660
Merge pull request #5666 from twokul/class-name-bindings

Fixes classNameBindings regression