In Ocata we changed use_neutron=True as the default. When configuring
Nova to use Neutron, one is supposed to set the firewall_driver
config option to nova.virt.firewall.NoopFirewallDriver, but that was
not the default. This change makes it the default to match the default
for use_neutron.
Change-Id: If012acdd0ef2a66948ae45288cccb766262efb68