Test Hive Impersonation in Livy

Previous attempts to get Livy working with hive impersonation have been unsuccessful. The cause was likely that hive sessions were not enabled in Livy, along with the other settings, see Livy users group https://www.mail-archive.com/user@livy.incubator.apache.org/msg00294.html

For this story, we need to ensure that impersonation does work. Once this task is complete, move directly to