WFLY-2693 list-active-jsf-impls missing reply type

The DMR operation "list-active-jsf-impls" of the JSF subsystem is
missing a reply type. Therefore the operation will show up as "Void"
in VisualVM and no result will be displayed.

 * set the reply type to list
 * set the reply value type to string
 * replace #withFlags with #setRuntimeOnly and #setReadOnly

Issue: WFLY-2693
https://issues.jboss.org/browse/WFLY-2693