Enable to configure and use the loopback multicast sockets (issue hazelcast/hazelcast#2594).
Update the XML configuration generator and builder, related to issue #2594.
Add unit tests related to the issue #2594.
Fixing the unit test of the multicast loopback mode.
Cleaning the code of the MulticastLoopbackModeTest class according to the recommendations of the Hazelcast's development team.
Resolve conflicts with the master branch
Fixing the style of the code.

According to the errors found by the code style checker, the code of the
multicast loopback feature is fixed.
Merge https://github.com/gallandarakhneorg/hazelcast
Merge branch 'master' of github.com:gallandarakhneorg/hazelcast
Cleanep and test fixes.