Updated openstack/openstack
Project: openstack/neutron  8f361a658fce478198f1a08c1689d636014e1ab2
null
Apply six for metaclass

__metaclass__ cannot be used in python3.
six be used in general for python 3 compatibility.

Change-Id: Ib0d71b9676dc01390679396443575c05975d3b58
Closes-Bug: #1236648