Better handle case when a domain has no DNS proxy set
When a domain in Foreman (More -> Domains -> dmz.example.com) does not have a DNS smart-proxy set, creating a host in that domain fails with an unhelpful error message like this: "Create DNS record for web01.dmz.example.com task failed with the following error: undefined method `create' for nil:NilClass".
Full log message here: http://pastie.org/4358270
A case like this should either result in a better error message (e.g. "No DNS smart proxy set for domain") or, probably even better, a warning that no proxy is set and thus no DNS RR (A) will be created for the new host. The user could then have the option to continue or fix the missing DNS proxy.