Prevent shadowing user-defined jgroups configuration file

When users create their own JGroups configuration file and name it the same way as default configuration files (jgroups-udp.xml / jgroups-tcp-xml / jgroups-ec2.xml), they might not be visible to the user application as they're shadowed by the default configuration files.

Proposed solution:

• place current jgroups configuration files into META-INF/configs folder (this folder doesn't have to have an obscure name such as "_internal" because of the following two points which complement the solution)
• define order in which the config files are read by class loader (i.e. first scan user application, then path under META-INF/configs)
• when Infinispan is started, log the path to the configuration file used, e.g.:

  2014-06-12 06:45:02,871 [thread-name] INFO  [package-name] Using JGroups configuration file 'jar:META-INF/example_configurations/jgroups/udp.xml'
  2014-06-12 06:45:02,871 [thread-name] INFO  [package-name] Using JGroups configuration file 'file:/app_home/config/jgroups-udp.xml'