[WFLY-1801] Improvements around worker-thread-pool/endpoint choice, plus WFLY-2865, WFLY-2589

Improves handling of legacy 'worker-thread-pool' config vs new 'endpoint' config, plus brings in 2 commits related to improving management transformation that are needed to handle this correctly

* Make worker-thread-pool/endpoint configs a choice in xsd
* Don't count on parser to add a default endpoint resource; do it in OSHs
* Have an OSH validate that both worker-thread-pool and endpoint aren't configured
*Transformation improvements:
-- same transformation for all previous versions
-- reject if any endpoint attributes are configured (requires WFLY-2865)
* Some test rationalization and improvement, plus restore a test previously removed