If /var/log/lxc exists, move it to the log aggregation parent

In https://review.openstack.org/344721 the log aggregation link
was added for lxc logs to ensure that the logs are collected
in a central place.

This patch ensures that any pre-existing folder (which may exist
due to the playbook being run when upgrading) is moved to the
right place. This ensures that previous logs are kept and that
upgrades execute without failure.

Change-Id: I35a9b3176a79caf9cee177442fa6b3d79e057ea9

playbooks/lxc-hosts-setup.yml

@@ -19,16 +19,24 @@
   max_fail_percentage: 20
   user: root
   pre_tasks:
-    - name: Create log dir
+    - name: Check the state of the default LXC service log directory
+      stat:
+        path: "/var/log/lxc"
+      register: _lxc_log_dir
+    - name: Move the existing folder to the log aggregation parent
+      command: "mv /var/log/lxc /openstack/log/{{ inventory_hostname }}-lxc"
+      when:
+        - _lxc_log_dir.stat.isdir is defined
+        - _lxc_log_dir.stat.isdir | bool
+    - name: Create the new LXC service log directory
       file:
         path: "/openstack/log/{{ inventory_hostname }}-lxc"
         state: directory
-    - name: Create log aggregation links
+    - name: Create the LXC service log aggregation link
       file:
         src: "/openstack/log/{{ inventory_hostname }}-lxc"
         dest: "/var/log/lxc"
         state: "link"
-        force: "yes"
   roles:
     - { role: "lxc_hosts", tags: [ "lxc-host", "host-setup" ] }
     - role: "rsyslog_client"