Decalre the dns variable in the defaults

For better usability put the variable name in the defaults, and then use
it in a playbook.

This follow the principle that every role variable should be in
defaults/main.yaml

Signed-off-by: Roy Golan <rgolan@redhat.com>

roles/openshift_ovirt/defaults/main.yml

@@ -6,6 +6,9 @@ wait_for_ip: true
 openshift_ovirt_cluster: Default
 template_name: openshift_node
 
+# User must provide the dns zone
+openshift_ovirt_dns_zone:
+
 # oVirt VM Profiles
 openshift_ovirt_vm_profile:
   master:

roles/openshift_ovirt/tasks/build_vm_list.yml

@@ -8,7 +8,7 @@
 - fail:
     msg: "The openshift_ovirt_dns_zone variable is required."
   when:
-  - openshift_ovirt_dns_zone is not defined
+  - openshift_ovirt_dns_zone is none
 - name: Create virtual machine list fact
   set_fact:
     vms: >-