Load configfs kernel module for iscsid

The configfs kernel module is not mounted by default in Ubuntu 16.04,
leading to the iscsid container failing to start because it bind mounts
/sys/kernel/config. The issue does not apply to Ubuntu 18.04, or other
distros (AFAIK), which load configfs by default.

This change loads the configfs module when the iscsid container is in
use.

Change-Id: I5b521ddca24b919658d2664ede2d878507d6d106
Closes-Bug: #1631072

ansible/roles/iscsi/tasks/config.yml

 ---
+- name: Load and persist configfs module
+  import_role:
+    role: module-load
+  vars:
+    modules:
+      - name: configfs
+  when: ( ( inventory_hostname in groups['compute'] or inventory_hostname in groups['cinder-volume'] ) and enable_cinder | bool and enable_cinder_backend_iscsi | bool )
+         or ( inventory_hostname in groups['ironic-conductor'] and enable_ironic | bool )
+
 - name: Ensuring config directories exist
   file:
     path: "{{ node_config_directory }}/{{ item }}"