Explicitly set jobs sfc and bgpvpn to ML2/OVS

Devstack is changing the Neutron default to OVN backend.
This patch makes sure that neutron-tempest-plugin-sfc and
neutron-tempest-plugin-bgpvpn-bagpipe jobs use OVS backend and starts
all neutron services like DHCP-agent and metadata-agent.

Change-Id: I1f0c718b19781fa491c1e75a08282b30cf77ba1e
1 file changed