Create 1.2.0 release notes
Create 1.2.0 release notes

Change-Id: I82dcd075960d9a4ed8b89471a31a951b274de4fa

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