Comment 12 for bug 1510680

1. Another solution (which of course should be avoided) is to omit
firewall_driver = neutron.agent.linux.iptables_firewall.IptablesFirewallDriver
in the [securitygroup] section of linuxbridge_agent.ini on compute node(s).

2. Not being able to spawn a VM is fatal.
I think this situation should be addressed as soon as possible.
Should it be reported as an error affecting mitaka precisely?
(stable/liberty is ok as mentioned above)