Handle adding and removing UDPU members atomically

When config file is reloaded with removed UDPU member, internal icmap
index of nodelist.node can change. This can result in removal and then
adding back node. This, with UDPU alive filtering (where member is by
default considered as not a member) makes corosync not sending messages
to such members resulting in new membership creation.

Solution is to properly test which members were really deleted and added
(instead of relying on internal and dynamic naming of icmap hash table
key name).

Also trully dynamic add and remove node (via cmap) is now handled by
same function so totem_config->interfaces is now updated properly.

Signed-off-by: Jan Friesse <jfriesse@redhat.com>
Reviewed-by: Fabio M. Di Nitto <fdinitto@redhat.com>