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: I20c84563b0a61fbc2c465cb52bdffc2f9031e3a8
Closes-Bug: #1808946

openstack/python-zaqarclient