Add missing package openstack-neutron-openvswitch

The section for configuring ML2 on the network node indicates that
the openvswitch and neutron-openvswitch-agent services should be
started.  These services require the installation of
openstack-neutron-openvswitch.

Change-Id: I08a7cb0f7bc739d6619df91f27a4c2cf236b8ded
Closes-Bug: #1307258