_member_ role is a long not used default keystone role,
for instance Horizon moved to use member role from yoga [1]

[1] https://docs.openstack.org/horizon/yoga/configuration/settings.html#openstack-keystone-default-role

Closes-Bug: #2038314
Change-Id: Idc9bce82c682e37c5bea10c93577091b85f3ad45