bug 924267: Explicitly set firewall_driver to nova.virt.libvirt.firewall.IptablesFirewallDriver

Because of https://bugs.launchpad.net/nova/+bug/924266, the default firewall_driver should
not be the libvirt's one. So set the driver explicitly.

Change-Id: I1e6a0d824e857bb082eef2a684445241d4c31aae
diff --git a/AUTHORS b/AUTHORS
index ec71326..dc12105 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -1,6 +1,7 @@
 Adam Gandelman <adamg@canonical.com>
 Andy Smith <github@anarkystic.com>
 Anthony Young <sleepsonthefloor@gmail.com>
+Armando Migliaccio <armando.migliaccio@eu.citrix.com>
 Brad Hall <brad@nicira.com>
 Chmouel Boudjnah <chmouel@chmouel.com>
 Dean Troyer <dtroyer@gmail.com>