Fix wrong command to define neutron firewall class

The firewall_driver option in the OVS configuration file was not properly
defined for rpm based distributions: the key word was missing in the
openstack-config command, and the section name was incorrect.

Change-Id: I5346b3ddb39ae961437f0b675043130a8a5dcb5f
Closes-Bug: #1281177
backport: none
Merge "Fix wrong command to define neutron firewall class"