UnknownTypeCollector: change in UnknownType.reportError() behaviour

to allow the metamodel to always report the error as an exception, while
we only want it once in the compiler
model loader: made it possible to plug custom error reporters for UnknownType so the metamodel can have one which always throws

With useful info rather than what we have now
CompilerTest: allow running both run/test comments in jboss modules #1572
Updated test for #1572