Fix instance where a domain id is indicated, but no hostname is given

The model was asking the proxy to try and create a record that looks like ".domain.com", and if you were trying to create a second host with the same characteristics (blank hostname, domain name non-nil) on its interface, the proxy would properly fail with a "Entity already exists" error.

This really only needs commit id https://github.com/pccowboy/foreman/commit/ecbc92fbfacb3ac493be63e900c8f7ded1b7989a - but even after merging from theforeman/develop I cannot seem to get a clean pull request from the github UI.  If someone can tell me how to get a clean copy of develop, I'll be happy to redo the request.