add test for no attribute type

from http://emberjs.com/guides/models/defining-models/:
"If you don't specify the type of the attribute, it will be whatever was
provided by the server. You can make sure that an attribute is always
coerced into a particular type by passing a type to attr:"
Merge pull request #2522 from kellyselden/add-no-attribute-type-test

add test for no attribute type
use defaultValue without supplying type

I prefer to use `DS.attr()` without a type when possible, but when I
want to use a defaultValue, I must supply a type. This would make it so
that you can supply a defaultValue, but still have an attribute without
a transform.