use common agent topics from neutron-lib

The neutron.common.topics module was rehomed into neutron-lib with
commit Ie88b84949cbd55a4e7ad06341aab77b286cdc485
This patch consumes it by using neutron-lib's version of the module in
prep for Ia4a4604c259ce862597de80c6deeb3d408bf0e95

Change-Id: I300f81cb4c93a485dfef4e7d8a1ad61d239dccf5

networking_arista/l3Plugin/l3_arista.py

@@ -15,6 +15,7 @@
 import copy
 import threading
 
+from neutron_lib.agent import topics
 from neutron_lib import constants as n_const
 from neutron_lib import context as nctx
 from neutron_lib.plugins import constants as plugin_constants
@@ -26,7 +27,6 @@ from oslo_utils import excutils
 from neutron.api.rpc.agentnotifiers import l3_rpc_agent_api
 from neutron.api.rpc.handlers import l3_rpc
 from neutron.common import rpc as n_rpc
-from neutron.common import topics
 from neutron.db import db_base_plugin_v2
 from neutron.db import extraroute_db
 from neutron.db import l3_agentschedulers_db