Various software on EDPM nodes expect an FQDN. We should require and add a validation that an FQDN is set. When one is not set, we should fail the EDPM deployment.

We shouldn't attempt to set an FQDN ourselves in the product if one isn't already set by the time we are running the ansible deployment. For preprovisioned, this means documenting the requirement, how to set one, and how to check one is set. For provisioned, an FQDN should be set automatically during baremetal provisioning (needs to be checked, I'm not sure of the current behavior).

There is also already a validation in the edpm-ansible role edpm_nodes_validation, but it's disabled by default due to edpm_nodes_validation_validate_fqdn defaulting to false. The validation also checks that the FQDN is in /etc/hosts, which is not necessarily required or always true (unless we document that and start making it true). I think the correct way to set the FQDN is likely with hostnamectl which should populate /etc/hostname. We likely should use hostnamectl and/or /etc/hostname in a new validation.