[WFLY-457] Replace mod_cluster proxy-list attribute with list of outbound socket bindings

https://issues.jboss.org/browse/WFLY-457

Needs https://github.com/wildfly/wildfly/pull/6420 merged first and then rebase.
Absolutely. Speaking of it will become quite wrong: in EAP 6.4, it will be deprecated *since* 1.5.0 model, in WF 8 and 2.0.0 model it will be fine and not deprecated and then again in WF 9 in 3.0.0 model it will be deprecated since. Oh well.