[FIX] XStream was not working

Welcome to the wonderful OSGi environment. XStream used the wrong class
loader to find the classes.

Change-Id: I49b568d1d9a6066df8feb5446d7706d2e0fcb262
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1369
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>