MODE-2399 Fixed the output structure for the default-initial-content configuration.

the logic which closes the `<workspaces>` element is already part of the code, a few lines below: https://github.com/hchiorean/modeshape/blob/MODE-2399/deploy/jbossas/modeshape-jbossas-subsystem/src/main/java/org/modeshape/jboss/subsystem/ModeShapeSubsystemXMLWriter.java#L177