Renamed image->image_name and flavor->flavor_name to avoid collisions

Change-Id: I09a133b5c4f6c71e10d274be1c70b7edcce1c83c

ci/roles/server_volume/tasks/main.yml

@@ -4,7 +4,7 @@
     state: present
     name: "{{ server_name }}"
     image: "cirros-0.5.2-x86_64-disk"
-    flavor: "{{ flavor }}"
+    flavor: "{{ flavor_name }}"
     network: "{{ server_network }}"
     auto_ip: false
     wait: true