Create LXC containers with a rootfs dir

Previously, an LXC container's rootfs was being placed into
/var/lib/lxc/<container>/rootfs.  Commit
https://review.openstack.org/#/c/190048/8 inadvertently changed this so
that a container's rootfs is now placed into /var/lib/lxc/<container/.
The downside here is that we now have a directory containing a
container's root fs and the LXC configuration for the container.

This change creates a new role-level variable called
lxc_container_rootfs_directory which defaults to
"{{ lxc_container_directory }}/{{ container_name }}/rootfs" and passes
this variable when creating the container.

Change-Id: Ibbaa879166f5efaf7ca96add131cc3762dd88653
Closes-Bug: #1470101

playbooks/roles/lxc_container_create/defaults/main.yml

@@ -21,6 +21,7 @@ lxc_container_template: ubuntu
 # lxc container rootfs directory and cache path
 lxc_container_directory: "/var/lib/lxc"
 lxc_container_cache_path: "/var/cache/lxc"
+lxc_container_rootfs_directory: "{{ lxc_container_directory }}/{{ container_name }}/rootfs"
 
 # container_fs.* is only used with building on an LVM backend
 lxc_container_fs_size: 5G

playbooks/roles/lxc_container_create/tasks/container_create.yml

@@ -57,7 +57,7 @@
     template: "{{ properties.container_template|default(lxc_container_template) }}"
     state: started
     backing_store: "{{ properties.container_backing_store|default(lxc_container_backing_store) }}"
-    directory: "{{ lxc_container_directory }}/{{ container_name }}"
+    directory: "{{ lxc_container_rootfs_directory }}"
     fs_size: "{{ properties.container_fs_size|default(lxc_container_fs_size) }}"
     fs_type: "{{ properties.container_fs_type|default(lxc_container_fs_type) }}"
     vg_name: "{{ properties.container_vg_name|default(lxc_container_vg_name) }}"