Provide an option to update the ShimLoader's classloader

- making this option default because it's equivalent to the old flat jar
- making it optional because we still debug how we miss the non-default
  classloader in #NVIDIA#3704 and it's not the right behavior for addJar with
  userClassPathFirst. However, I think we shoudl generally stop
  documenting --jars as the plugin deploy option

Fixes NVIDIA#3704

Signed-off-by: Gera Shegalov <[email protected]>