[WFLY-1801] Improvements around worker-thread-pool/endpoint choice
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