Fixed entity metadata resolution.

The current code assumes that an entity will always have a corresponding
LDAPObject on the server, so it looks for the metadata in a fixed location.
This assumption doesn't work for HBAC Test since it is a Command, not an
LDAPObject, so the metadata has to be obtained from a different location.
A new method get_default_metadata() has been added to allow each entity
to find the metadata from the correct location.

Ticket #388

install/ui/ipa.js

@@ -191,14 +191,12 @@ var IPA = function() {
 
             builder.entity({
                 factory: factory,
-                name: name
+                name: name,
+                builder: builder
             });
 
             var entity = builder.build();
-
-            entity.init({
-                builder: builder
-            });
+            entity.init();
 
             return entity;