Allow to let puppet-keystone managing _member_ role which is required
by Horizon. Can be enabled with keystone_enable_member parameter (disabled
by default.)
A patch in tripleo-heat-templates will activate this boolean to true so
Horizon deployments will trigger the role creation.
Change-Id: I5272f1fc199772043db48d29b0ea99a8bfff4ed5
Related-Bug: #1741066