Don't reuse dns_info_record (fix for recreating jobs)

This change prevents to reuse the stored dns_info_record, so it will
return the info fetched from the latest agent get_state call.

When recreating a job, instance updater tries to guess what changes
are needed to apply before recreating the vm. If we store the dns
info into an instance variable and later, when we delete/create
the vm again, there's a change in its IP address, dns record will
return the older IP address instead of the new one.