Add default API version for magnum service
Add default API version for magnum service

shade is adding magnum support, so we should probably grow a default
value for the container_api_version.

Change-Id: I2551f2921f10ba109ccb52301cc8ad23c5f81c46

stackforge/python-openstacksdk,openstack/python-openstacksdk,stackforge/python-openstacksdk,dtroyer/python-openstacksdk,openstack/os-client-config,dtroyer/os-client-config,dtroyer/python-openstacksdk,openstack/python-openstacksdk