Update a RBAC Policy.

    :param request: request context
    :param policy_id: target policy id
    :param target_tenant: target tenant of the policy
    :return: RBACPolicy object

def rbac_policy_update(request, policy_id, **kwargs):
    """Update a RBAC Policy.

    :param request: request context
    :param policy_id: target policy id
    :param target_tenant: target tenant of the policy
    :return: RBACPolicy object
    """
    body = {'rbac_policy': kwargs}
    rbac_policy = neutronclient(request).update_rbac_policy(
        policy_id, body=body).get('rbac_policy')
    return RBACPolicy(rbac_policy)