Always register api.domain with the router

* api.domain will always reach the cloud controller.
* Any existing prefixes will also be registered so they will work too.
* Manifests that use ccng will continue to work with both ccng.domain and
api.domain with no changes.
Add test for register_routes
Merge pull request #34 from cloudfoundry/api_host_default

Always register api.domain with the router