Use the jboss.server.lib.url property in the conf/jboss-service.xml classpath

As noted in JBDOCS-24, although we reference a system property jboss.server.lib.url this is really a read-only property that cannot be set externally to have any effect. However, if the conf/jboss-service.xm classpath explicitly used this property:

<classpath codebase="${jboss.server.lib.url}" archives="*"/>

you have the same behavior as currently with the ability to override the server library location using the jboss.server.lib.url property.