create routes with empty host-names to enable use of private shared domains

[freudl]

app-broker should enable me to create routes by omitting hostnames as long as there is a domain specified.

cf cli enables me to do so, but app-broker does not.

Rationale of omitting hostnames: cf enables an operator to share private domains and, therefore, provide organizations access to dns segments.

cf create-route my-app.example.com --path /api is a valid command and results in this route: my-app.example.com/api.
App-broker, in contrast, cannot do so.