Define context.roles with base class
Define context.roles with base class

In f383bd2973c58c5272504603e4f9dddd55c5bb68, oslo.context (2.2.0)
added roles support in the context itself. This passes roles to
super()__init__.

Change-Id: I39e7b6cd6c57afbd656d69ad50a3d50ed9813254

openstack/designate,openstack/designate,openstack/designate