Ensure DIB_ETC_HOSTS_EXTRA is defined

Author: Alex-Welsh

etc/kayobe/stackhpc-overcloud-dib.yml

@@ -47,6 +47,8 @@ stackhpc_overcloud_dib_env_vars:
   # sometimes).
   # DIB_DISTRIBUTION_MIRROR: "{{ stackhpc_repo_ubuntu_focal_url if os_distribution == 'ubuntu' else '' }}"
   DIB_DRACUT_ENABLED_MODULES_DEFAULT_CONFIG: "{{ stackhpc_overcloud_dib_dracut_enabled_modules_default_config }}"
+  # NOTE: DIB_ETC_HOSTS_EXTRA must be defined and cannot be an empty string 
+  DIB_ETC_HOSTS_EXTRA: "#"
   DIB_RELEASE: "{{ overcloud_dib_os_release }}"
   DIB_SUDOERS_FILENAME: "no-fqdn"
   # Avoid DNS queries during sudo commands, since we might not always have working DNS.