Fix Config stub to not conflict with spec_helper

Only define the minimal Config stub if it's not already defined,
to avoid overriding the real Config class when spec_helper is also loaded.

Author: johha

spec/lightweight_spec_helper.rb

@@ -8,13 +8,16 @@
 module VCAP
   module CloudController
     # Minimal Config stub for message validation specs
-    class Config
-      def self.config
-        @config ||= new
-      end
+    # Only define if not already defined (avoid conflict with spec_helper)
+    unless defined?(Config)
+      class Config
+        def self.config
+          @config ||= new
+        end
 
-      def get(*_keys)
-        nil
+        def get(*_keys)
+          nil
+        end
       end
     end
   end