Update mailinglist from dev to discuss
Update mailinglist from dev to discuss

openstack-dev was decomissioned this night in https://review.openstack.org/621258
Update openstack-dev to openstack-discuss

Change-Id: Ib99d827f6c24891f44a983529bbe45cfba50da29

openstack/openstack-ansible-galera_client,openstack/openstack-ansible-galera_client