Add release notes for 1.7.0
Add release notes for 1.7.0

Change-Id: I4b4d229f7c3292923c8a29d1e1182a8352688b5d

dtroyer/python-openstackclient,redhat-openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,openstack/python-openstackclient,BjoernT/python-openstackclient,BjoernT/python-openstackclient,redhat-openstack/python-openstackclient