WFLY-2772 Leverage JGroups FORK protocol to consolidate EE channels

https://issues.jboss.org/browse/WFLY-2772

By default, web, EJB, and JPA clustering layers now use a single JGroups channel.
Channels are now enumerated in the model, rather than created implicitly via the Infinispan subsystem.

Requires fix contained in JGroups 3.4.6.Final.
https://issues.jboss.org/browse/WFLY-3848

Also fixes deprecated HttpClient usage in clustering testsuite.
This needs to be undone in ChannelRemoveHandler, using MRR.unregisterOverrideModel.