remove knowledge of ntpserver config location from core agent
move knowledge of VCAP base dir from bundle collection to app
remove unused method from get_task

This was a hold over from before the action runner refactor
extract VCAP_BASE_DIR and other constants

Signed-off-by: Tim Jarratt <tjarratt@pivotallabs.com>
Extract drain script provider from drain action

Signed-off-by: Jeffrey Peckham <peckham@pivotallabs.com>