test_l3_dvr_db: switch to OVO for Agent
test_l3_dvr_db: switch to OVO for Agent

Change-Id: I42609b1c5aa2e15f240ed2108fd8b5ed445d350a
Partially-Implements: blueprint adopt-oslo-versioned-objects-for-db

mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron,huntxu/neutron,noironetworks/neutron,mahak/neutron,eayunstack/neutron,openstack/neutron,huntxu/neutron,noironetworks/neutron,eayunstack/neutron