Fix validations unit test to pass legitimately

Previously the unit test passed but the test was not correct.  The test was:

```
it "should be valid" do
  @object.should_not be_valid
end

```

This test did pass however because the delegation method on the 'swank' attribute did not have `unique: true` set.  

In this request I have set `unique: true` and changed the validation to ensure `@object` is valid.

The test passes and has been run with `rake active_fedora:ci`.