Fix java_jmx_server exploit

Add test case when discovering RMI endpoint as the previous one was not complete

Author: Philippe Tranca

modules/exploits/multi/misc/java_jmx_server.rb

@@ -196,7 +196,7 @@ def discover_endpoint
     ref = send_registry_lookup(name: datastore['JMXRMI'])
     return nil if ref.nil?
 
-    unless ref[:object] == 'javax.management.remote.rmi.RMIServerImpl_Stub'
+    unless ref[:object] == 'javax.management.remote.rmi.RMIServer' || ref[:object] == 'javax.management.remote.rmi.RMIServerImpl_Stub'
       vprint_error("JMXRMI discovery returned unexpected object #{ref[:object]}")
       return nil
     end