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: I31002589bc11e6b6786204a6c642a39b5924f166

openstack/openstack-ansible-repo_server,openstack/openstack-ansible-repo_server