Add mocked response for riak clusters.
user
```ruby
module Overriaktion
  module MockedResponses
    RIAK_CLUSTERS = '[{"created_at":"2011-10-10T03:31:34Z","id":1,"name":"Localhost","updated_at":"2011-10-10T03:31:34Z","user_id":1}]'
  end
end
```
assistant