[LIVY-889] Adding jars to Spark Interpreter classpath on an already running Livy Session

[praneetsharma]

What changes were proposed in this pull request?

• addJar invoked for a running Livy session will add that jar resource to SparkInterpreter classpath in addition to Spark driver classpath.
• addJarOrPyFile signature changed to return the local path to which it was copied. This local path is required to add the same jar resource to SparkInterpreter classpath.
• addFile now goes through appropriate Interpreter based on the interpreter instead of default PythonInterpreter.

https://issues.apache.org/jira/browse/LIVY-889

How was this patch tested?

This patch was tested by adding a Jar on a running Livy session and then trying to load a class from that jar using spark interpreter.