Livy interpreter session auto restart doesn't work with livy 0.6.0

Livy 0.6.0 changed the error messages from being text strings to being json. Specifically the error for a missing session went from `"Session '7' not found."` to `{"msg":"Session '7' not found."}`. There is a hard coded regex match in the BaseLivyInterpreter class that now fails to match. As a result instead of a session auto restarting the following error message is displayed: "No rest api found for http://spark-livy.spark-analytics.svc.cluster.local:8080/sessions/7/statements, 404."