Cassandra Automated Upgrade Testing Improvements

The Cassandra Test Engineering team has been working to improve testing for the Cassandra upgrade process, with a focus on making sure nodes can use the latest releases' improvements without any negative impact on pre-upgrade data. They have made changes to their open-source python project, cassandra-dtest, which is run on a publicly accessible Jenkins server found at cassci.datastax.com. The team has simplified the test upgrade procedure, extended it to as many scenarios as practical, and minimized human intervention in keeping tests updated. They have also implemented a system that allows tests to automatically see new minor version releases and test them without any code changes needed.