Fix issue with new oslo.messaging

As oslo.messaging 1.3.0.a7 was released, there was change
https://review.openstack.org/62931 merged to it. It caused
intersection issue between openstack.common.service.Service
and oslo.messaging.MessageHandlingServer classes both used
in Climate (no periodic tasks running as symptom here).

This change fixes that, working both with oslo.messaging 1.3.0.a7
and previous versions.

Change-Id: Icb7d88d4a0cb1ed568b731ca9716982eb8ffb092
Closes-Bug: #1281521
Merge "Fix issue with new oslo.messaging"