Use ml2_conf.ini in neutron-openvswitch-agent

This change switches the neutron-openvswitch-agent service to use the
ml2_conf.ini configuration file instead of ovs_neutron_plugin.ini.

Some required options were missing from the ml2_conf.ini template, so
those have been added.  The template for ovs_neutron_plugin.ini has been
removed since it is no longer used.

Co-authored by: James Slagle <jslagle@redhat.com>
Change-Id: Iabfd8a33d58d4f45de24310211829cedbae001dd
Merge "Use ml2_conf.ini in neutron-openvswitch-agent"