totem: Inform RRP about membership changes

Services are informed about membership changes, but if same information
is needed inside totemrrp or totemnet, it's impossible to gather this
information.

Patch makes this possible for now only for RRP with empty callbacks.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>