adding else statement with empty string

starting ansible 2.X it require a else statement.

Closes-bug: #1588941
Change-Id: I3f12be8de75ddcebf28a077c361a9206b36aafb0

ansible/group_vars/all.yml

@@ -239,12 +239,11 @@ kibana_user: "kibana"
 #################################
 # Cinder - Block Storage options
 #################################
-cinder_volume_driver: "{{ 'ceph' if enable_ceph | bool }}"
-cinder_volume_driver: "{{ 'lvm' if enable_iscsi | bool }}"
-cinder_volume_group: "{{ 'cinder-volumes' if enable_iscsi | bool }}"
-cinder_volume_backend_name: "{{ 'cinder-volumes' if enable_iscsi | bool }}"
-cinder_iscsi_helper: "{{ 'tgtadm' if enable_iscsi | bool }}"
-cinder_iscsi_protocol: "{{ 'iscsi' if enable_iscsi | bool }}"
+cinder_volume_driver: "{{ 'ceph' if enable_ceph | bool else 'lvm' }}"
+cinder_volume_group: "{{ 'cinder-volumes' if enable_iscsi | bool else '' }}"
+cinder_volume_backend_name: "{{ 'cinder-volumes' if enable_iscsi | bool else '' }}"
+cinder_iscsi_helper: "{{ 'tgtadm' if enable_iscsi | bool else '' }}"
+cinder_iscsi_protocol: "{{ 'iscsi' if enable_iscsi | bool else '' }}"
 
 ###################
 # Ceph options