Refactor the way we register transformers for jgroups and infinispan sub...

...systems - enclosing if-s is not necessary

@pferraro, here it is as promised, it was only 3 occurences (continuation of https://github.com/wildfly/wildfly/pull/6372)

We agreed it's worth having to evaluate several more if statements when registering transformers rather than with every new model version having to indent entire transformation block which makes the change log significantly larger, make git blaming complicated and making rebasing painful.