Eliminate redundant testing in JGroups and Infinispan subsystem tests

The JGroups and Infinispan subsystems have subclasses of AbstractSubsystemBaseTest that include @Test method that essentially duplicate parts of what the superclass testSubsystem does. These subclasses execute the test for numerous xml versions, so the duplication isn't just run once. So, remove that.

In the infinispan case removing it saves about 10s on my laptop, but more importantly it saves about a minute on Windows runs on ci.wildfly.org. The long execution time on CI is what drew my attention to this.