FILE_PING.interval was set lower for testing purposes but this seems to contribute to chattiness. https://issues.jboss.org/browse/JGRP-1538
[RM-1523] Circumvent UDP problems reported on CentOS by using a FILE_PING variant to discover cluster members. Unless overridden in the usual way with $JENKINS_HOME/jgroups.xml, $JENKINS_HOME/jgroups/ is now used for discovery and $JENKINS_HOME/cluster-identity.txt is no longer used since the file path determines the identity. (Also fixes [RM-1500] warnings about packet sizes.)
[RM-1522] discard_incompatible_packets="false" so that it is just a warning if a user mixes different versions of jGroups between jenkins.war and jenkins-ha-monitor.jar.
HASingleton.demote is not called idempotently, so we need to emulate the behavior of Main in the proxy WAR.
TCP version of the protocol
Java 5 is not supported by this version of high availability. Use JENKINS_HA=false to disable.