Fix AttributeError for calling _register_as_publisher
Fix AttributeError for calling _register_as_publisher

Change-Id: I17f785efbec15be306c9f7d7f629b9ec6f50c91a
Closes-Bug: #1567853

FrankDuan/df_code,openstack/dragonflow,FrankDuan/df_code,FrankDuan/df_code,openstack/dragonflow,openstack/dragonflow