[WFLY-2291] Update messaging XML namespace to 2.0 

The XML namespace for the messaging subsystem was erroneously bumped
from 1.3 to 1.4 for WildFly 8.

This is an error as the 1.x version must be reserved for AS7 7.x releases.
WildFly 8 must use a 2.0 namespace.

+ refactoring of test for messaging resource transformers