setup_haskell_sandboxes.rb: refactor out classify_haskell_packages function
setup_haskell_sandboxes.rb: refactor out classify_haskell_packages function

classify_haskell_packages classifies Haskell packages into 3 categories:
1. Installed
   - Already installed. No further action required
2. ErrorFileExists
   - A file with the same name as the destination directory of the package
     exists. Will not proceed with package installation
3. Pending
   - Package has not been installed; will install it

This slightly cleans up the logic in the setup_haskell_sandboxes function

Signed-off-by: Yan Han Pang <2a3dbd0474bc7e70adfd773b05f6c3249124ff3d@users.noreply.github.com>

yanhan/bin-src,yanhan/bin-src,yanhan/bin-src,yanhan/bin-src