The task 'rake license:generate-notice-file` Should also take into consideration jars

Before any releases of Logstash we are running a script to generate the "NOTICE.TXT" file, this file contains the list of all the plugins or library shipped with Logstash and their corresponding license.

The problem is this file only contains the license from the ruby side and not from the java side.
Since we are writing more and more java we need to update the script to also include the license from the included jars.