update galera cluster database bind mount dirs

With the current play we cannot over-ride the
```/openstack/{{ inventory_hostname }}``` host directory for bind
mounting database directory. Updated it so that user can specify
a particular host direcotry of his choice.

Change-Id: I29115b048cc7c65f55217fbe2abf7f4e954a0e5e

playbooks/galera-install.yml

@@ -27,9 +27,7 @@
             dest: "/var/log/mysql_logs"
     - include: common-tasks/os-lxc-container-setup.yml
       vars:
-        list_of_bind_mounts:
-          - bind_dir_path: "/var/lib/mysql"
-            mount_path: "/openstack/{{ inventory_hostname }}"
+        list_of_bind_mounts: "{{ galera_container_bind_mounts }}"
         extra_container_config_no_restart:
           - "lxc.start.order=99"
     - include: common-tasks/package-cache-proxy.yml

playbooks/inventory/group_vars/galera_all.yml

@@ -17,3 +17,8 @@ galera_client_drop_config_file: true
 
 # Ensure that the package state matches the global setting
 galera_server_package_state: "{{ package_state }}"
+
+# Galera default list of bind mounts
+galera_container_bind_mounts:
+  - bind_dir_path: "/var/lib/mysql"
+    mount_path: "/openstack/{{ inventory_hostname }}"