[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.
Instead of context.isNormalServer(), use context.getProcessType().isServer(). The "normal" part isn't relevant -- using this config on a server started with --admin-only is also incorrect.