Zun: fix Cinder (volume) iSCSI support

Fixes /dev volume, missed in the previous commit [1].
iscsid was installing the devices in /dev but zun-compute
could not see them due to the emulated /dev volume.

[1] I2c4aa666ff9f952e32c450347d31ddbf2e58209e

Change-Id: Ic72c910b92765b9a6f59224728e9c4ea2482bc5a
Related-bug: #1797448
Related-bug: #1848933

ansible/roles/zun/defaults/main.yml

@@ -96,6 +96,7 @@ zun_compute_default_volumes:
   - "/usr/lib/docker:/usr/lib/docker"
   - "/var/lib/docker:/var/lib/docker"
   - "/lib/modules:/lib/modules:ro"
+  - "/dev:/dev"
   - "{% if enable_iscsid | bool %}iscsi_info:/etc/iscsi{% endif %}"
 
 zun_extra_volumes: "{{ default_extra_volumes }}"