Make it easier to find logs for failing tests in cluster_test

When looking at MB-58120 the build artifact contained logs for all clusters that had previously been run by the test, 9 in total. Only one set of logs was relevant to the failure that was reported. It would be beneficial if we could either delete the cluster logs when we shut them down (provided there are no errors) or perhaps rename the cluster logs to the test suites that they are associated with such that one does not have to scroll up from the failure in the test log to work out which cluster was being run/which set of logs is relevant.