Handle ports with no 'created_at' attribute
Handle ports with no 'created_at' attribute

Change-Id: I1ff4635365acd803878212787fa98c622c69a41b

dtroyer/python-openstacksdk,openstack/python-openstacksdk,openstack/python-openstacksdk,dtroyer/python-openstacksdk,stackforge/python-openstacksdk,openstack-infra/shade,stackforge/python-openstacksdk,openstack-infra/shade