Allow tripleo_firewall to work in check mode

Currently, there is a task that fails in check mode because it tries to
loop over stdout_lines which don't exist when running in check (the
command taks didn't actually run in check, so there is no stdout).

Change-Id: Ic569b15e0b866167c2a7e57dc26591fa8a2f6caa

tripleo_ansible/roles/tripleo_firewall/tasks/main.yml

@@ -109,5 +109,6 @@
         state: absent
         regexp: '^((?!.*comment)(?=.*(ironic-inspector|neutron-)))'
       when:
+        - not ansible_check_mode|bool
         - item.find('v=' ~ '^/') == -1
       loop: "{{ neutron_rules.stdout_lines }}"