WIP: pacemaker traffic optionally on a different network

The variables $lb_backend_server_names/addrs still define the "management" network.  pacemaker and galera traffic now occurs on a new network defined by $pcmk_server_names/addrs, AKA the "cluster management" network.  Optionally, $pcmk_server_names/addrs may have the same values as $lb_backend_server_names/addrs (i.e., use the same network for the management and cluster management networks).

Footnote: the pacemaker galera resource agent assumes that galera hostnames (used in the galera cluster configuration value wsrep_cluster_address) are consistent with pacemaker members, so for now we have no choice but to be consistent with that assumption, that interal galera and pacemaker traffic occur on the same network.