Update firewall_driver for Icehouse

While default value is merged:
https://review.openstack.org/93825

Signed-off-by: Emilien Macchi <emilien.macchi@enovance.com>

spec/classes/cloud_network_metadata_spec.rb

@@ -79,7 +79,8 @@ describe 'cloud::network::metadata' do
           :mechanism_drivers      => ['openvswitch','l2population'],
           :tunnel_id_ranges       => ['1:10000'],
           :network_vlan_ranges    => ['physnet1:1000:2999'],
-          :enable_security_group  => true
+          :enable_security_group  => true,
+          :firewall_driver        => 'neutron.agent.not.a.real.FirewallDriver'
       )
     end