When the association being passed to make!, machinist should not instantiate it

Given I have these blueprints as follow:

```
Company.blueprint do
end

User.blueprint do
   company
end
```

Then a call to `User.make!` will create a company as well.
However, if I do this: `User.make!(:company => my_company)`, Machinist still create another company aside `my_company`, which is a redundant company.
