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

Conflicts:
	mod_cluster/extension/src/main/java/org/wildfly/extension/mod_cluster/ModClusterExtension.java
	mod_cluster/extension/src/test/resources/org/wildfly/extension/mod_cluster/subsystem_2_0-reject.xml
Code cleanup especially around the logger (comment out unused methods, javadoc, formatting)
[WFLY-457] Restore 'proxy-list' attribute to be able to use EAP 6.x slaves
[WFLY-2527] Add some better documentation of what the test is doing
Merge pull request #6498 from rhusar/WFLY-457_proxy_list_outbound_basedon_WFLY-1970-rebase2

[WFLY-457] Replace mod_cluster proxy-list attribute with list of outbound socket bindings
Merge pull request #6632 from bstansberry/desc_WFLY-2527

[WFLY-2527] Add some better documentation of what the test is doing