ISPN-4867 Single event marshaller support more clearly defined in API

* Based on Dan's feedback, Hot Rod server API made it look as if you
could pass a per-factory marshaller but that's not really the case.
A single event marshaller is currently supported.
ISPN-4870 Upgrade to JGroups 3.6.0.Final
ISPN-4913 Add a SKIP_INDEXING flag to HotRod for symmetry with embedded
ISPN-4914 Don't print spurious warning about the isolation attribute on
server startup
ISPN-4911 Add DMR operation for invoking the Mass Indexer
ISPN-4916 Add MassIndexer, XSite State Transfer and Partitioning
ops/attributes to the server RHQ plugin
ISPN-4802 Make HotRodConcurrentStartTest more robust

* Since the method starts Hot Rod servers, it should take
responsibility to kill them too.
* Increased timeout for creating Hot Rod server.
* Use fork() method so that thread naming is correctly set.
* Finally, use Try() as a cleaner way to deal with failures
of either of Hot Rod server startups.