Mount /lib/modules folder for cinder-volume container

When using cinder lvm backend storage driver, lvcreate will load dm_*
linux modules when need. So /lib/modules is needed by cinder_volume
container.

Change-Id: I80985794d6aaa6b4ddc71680a97e0d07085dafa7
Closes-Bug: #1684378

ansible/roles/cinder/defaults/main.yml

@@ -31,6 +31,7 @@ cinder_services:
       - "{{ node_config_directory }}/cinder-volume/:{{ container_config_directory }}/:ro"
       - "/etc/localtime:/etc/localtime:ro"
       - "/dev/:/dev/"
+      - "/lib/modules:/lib/modules:ro"
       - "/run/:/run/:shared"
       - "{% if enable_iscsid | bool %}cinder:/var/lib/cinder{% endif %}"
       - "{% if enable_iscsid | bool %}iscsi_info:/etc/iscsi{% endif %}"