Upgrade to JGroups 4.1.8.Final

JGroups 4.1.8.Final includes fixes for two LOCAL_PING issues that affect our test suite:

• JGRP-2395 LOCAL_PING fails when 2 nodes start at the same time
• JGRP-2398 LOCAL_PING should remove local PingData on stop

The upgrade will allow us to remove the workaround for JGRP-2398 (GMS.num_join_attempts="1"), which is causing random failures in InitialClusterSizeTest.

 java.util.concurrent.ExecutionException: org.infinispan.manager.EmbeddedCacheManagerStartupException: 
org.infinispan.util.concurrent.TimeoutException: ISPN000399: Timeout while waiting for 4 members in cluster. Last view had [InitialClusterSizeTest-NodeD-26330, InitialClusterSizeTest-NodeC-48323]