Add stage_in() method on pilot.

This allows one to stage (shared) files to the resource the pilot is running
on.
This can either be in the "special" staging area or a regular place on the file
system.
Make use of new stage_in() method.
Use SETTING for use in other places.
Convert single entries into a list for ease.
Catch unknown type.
Use "configurable" location of staging area.
Create staging directory if it doesn't exist yet.
Cleanup examples.