Test adopted dogs can't be shown as an adoptable dog

[kasugaijin]

adoptable_dogs_controller.rb show action will take a user to /adoptable_dogs/:id unless the dog is adopted. In that case the user is redirected with a flash.

Acceptance criteria:

• test shows that trying to access show action in adoptable_dogs controller using an id of an adopted dog causes a redirect with flash.
• all tests pass.
• add the test to adoptable_dog_show_test.rb

[Overlandcoder]

I'd love to tackle this next!

[kasugaijin]

Close by #105