I think your configuration should look more like this:
We currently do not support any 'expressions' in arquillian.xml or override via System properties, but this is planned. Currently you would have to rely on Mavens resource filters.
I can work-around until that is supported. Keep up the great work!
That config was pulled out of Dan's jboss-javaee6-webapp 1.0.1.CR1 archetype.