Adds a role for a user on a tenant.

def add_tenant_user_role(request, project=None, user=None, role=None,
                         group=None, domain=None):
    """Adds a role for a user on a tenant."""
    manager = keystoneclient(request, admin=True).roles
    if VERSIONS.active < 3:
        manager.add_user_role(user, role, project)
    else:
        manager.grant(role, user=user, project=project,
                      group=group, domain=domain)