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: I34fb241499445e2a462b10815a26b79bded0fb78