Avoid building Spring Bus when deployment has no spring descriptor

The DescriptorDeploymentAspect currently relies on Spring availability in the classloader for deciding to generate a default jbossws-cxf.xml. Generally speaking, we should probably go the "Spring" way only when the deployment comes with a jbossws-cxf.xml (and spring is actually available ), so the user explicitly asked for that.

We might even evaluate changing the logic in JBossWSBusFactory to avoid using Spring when no spring descriptor is found (basically the same the CXF 2.4 SpringBusFactory does in public Bus createBus(String cfgFiles[], boolean includeDefaults) and we override in our JBossWS version of that factory).