Updated openstack/openstack
Project: openstack/taskflow  025fed8bf5f2b3c415b1aeb6e6fd8faf65869702

Just assign a empty collection instead of copy/clear

Instead of copying the '_events_listeners' then clear
them to get a clean copy just set the copies '_events_listeners'
to a new collection in the first place.

Change-Id: I17d4f02241c90a49fc4334cfd1f2fffd03d58927