Gate fix: Remove import neutron.plugins.ml2.config
Gate fix: Remove import neutron.plugins.ml2.config

Fix ml2 plugin config import Commit
Ibc5a9ab268578c243ef13f7e0041bacd6c0c410b moved the ml2 plugin config
file, which breaks unit tests

Depends on same fix in networking-sfc

Change-Id: I0033bb502cae0d668dbe8d420fd7986adb72ebb4
Depends-On: Ib7541abb0bee619b87fbcc7fee5d5095255e1ec7
Closes-Bug: #1716978

openstack/dragonflow,openstack/dragonflow,openstack/dragonflow