Subsystem test framework tweaks

Instead of having all the .dmr files stored in the org.jboss.as.subsystem.test package in subsystem-test/framework, have the subsystems generate them on demand as needed. The generation is only done once per test run, and should also allow people to store the .dmr in the test resources using the same package as the test (the main reason for that is that I think there were some very rare cases where we needed to touch up the resource definition although that is probably for pre-resourcedefinition, i.e. 7.1.x)