Updated openstack/openstack
Project: openstack/neutron  18d0977b7a37b44444d222ca4e437933a7135433

Removed unused iso8601 dependency

It should have been removed when migrating to oslo.utils when we dropped
timeutils module from our tree.

Change-Id: I4093a3c8faf3da5790ee31fdebec0b8ed70f84f3