Fix wrong assertion methods in a unit test
Fix wrong assertion methods in a unit test

Fix wrong assertion methods in the
test_delete_port_binding_delete_binding_and_levels method in
neutron.tests.unit.plugins.ml2.test_plugin.TestMl2PluginOnly.

Change-Id: Ib9c5f9ba660484df6048238375bc31f624228677
Closes-Bug: 1928471
Signed-off-by: Takashi Natsume <2c48eb5bf73c355a2d5583bc776dffa383cdf819@gmail.com>

openstack/neutron,mahak/neutron,mahak/neutron,openstack/neutron,openstack/neutron,mahak/neutron