Allow lxc_container_base_name to be set by the deployer

This patch ensures that the deployer is able to override the base
container name used when implementing copy-on-write based containers.

This patch ensures that the var name and default value matches that
set in https://review.openstack.org/358340

Change-Id: I672a77248061c00233fb306a25adbfe9add2c05d

defaults/main.yml

@@ -42,6 +42,10 @@ lxc_container_default_bind_mounts:
   - host_directory: "/openstack/backup/{{ inventory_hostname }}"
     container_directory: "/var/backup"
 
+# When using a base container to snapshot from for the overlayfs or LVM
+# copy-on-write backing stored, the base container can be set.
+lxc_container_base_name: "{{ lxc_container_map.distro }}-{{ lxc_container_map.release }}-{{ lxc_container_map.arch }}"
+
 # Mappings from Ansible reported architecture to distro release architecture
 lxc_architecture_mapping:
   x86_64: amd64

tasks/container_create.yml

@@ -94,7 +94,7 @@
 - name: Create container (copy-on-write backing store)
   command: >
     lxc-copy --snapshot -B {{ lxc_container_backing_store }}
-    --name {{ lxc_container_map.distro }}-{{ lxc_container_map.release }}-{{ lxc_container_map.arch }}
+    --name {{ lxc_container_base_name }}
     --newname {{ inventory_hostname }}
     -L {{ properties.container_fs_size | default(lxc_container_fs_size) }}
     --logfile {{ lxc_container_log_path }}/lxc-{{ inventory_hostname }}.log