ISPN-3375 Map/Reduce jobs with small value sizes fail because of timeouts putting intermediate keys into the cache

https://issues.jboss.org/browse/ISPN-3375

When the number of intermediate values per key is large, split list the
values in chunks based on stateTransfer.chunkSize.

Since the JGroups configuration used by the M/R test didn't seem "optimal", I've updated the JGroups configurations include in the distribution as well.