test_l3_odl: use odl l3 plugin, not neutron's
test_l3_odl: use odl l3 plugin, not neutron's

test_l3_odl didn't test l3_odl.
it should test l3_odl.

Change-Id: I74e14e840567057f99d7483221abcd1eced23e80

openstack/networking-odl,openstack/networking-odl,openstack/networking-odl