Only randomize the URI once

lib/msf/core/exploit/remote/java/http/class_loader.rb

@@ -27,10 +27,11 @@ module ClassLoader
   end
 
   def resource_uri
+    return @resource_uri if @resource_uri
     # the resource URI must end in / for the class loading to work
     path = super
     path += '/' unless path.end_with?('/')
-    path
+    @resource_uri = path
   end
 
   def on_request_uri(cli, request)