Jar handlers don't cleanup temporarily extracted jars

The jar handlers create a PackagedProgram when running a job or retrieving the execution plan. When a PackagedProgram is created and jars contained within a jar are automatically extracted to a temporary directory.

This directory is not automatically cleaned up; this must be done manually. The CliFrontend does that within #run, but the jar handlers do not, leading to jars piling up in the filesystem.