Stabilize some intermittently failing clustering tests

Some of the clustering tests

org.jboss.as.test.clustering.cluster.ejb.stateful.StatefulTimeoutTestCase(SYNC-tcp).timeout
org.jboss.as.test.clustering.cluster.ejb.stateful.StatefulFailoverTestCase(SYNC-tcp).nestedBeanFailover
org.jboss.as.test.clustering.cluster.singleton.SingletonTestCase(SYNC-tcp).testSingletonService
are failing due to OOM

ERROR [org.infinispan.topology.ClusterTopologyManagerImpl] (transport-thread-4) ISPN000230: Failed to start rebalance for cache default-host/stateful-failover: java.lang.OutOfMemoryError: unable to create new native thread