Use is_valid_ipv6() from oslo.utils
Use is_valid_ipv6() from oslo.utils

oslo.utils contains is_valid_ipv6() function, so we can reuse it.

Change-Id: Ib5898486ab79b9103edd2cd16f9a7b71b409b4f0

cpallares/glance_store,cpallares/glance_store,saeki-masaki/glance_store,redhat-openstack/glance_store,openstack/glance_store,jamielennox/glance_store,openstack/glance_store,jamielennox/glance_store,redhat-openstack/glance_store,saeki-masaki/glance_store