Some ideas for processors/grepper.py

[rgayon]

• [ ] Delete the temporary directory in cleanup()
• [ ] Doctring says """"Execute the grep command""" though that's not happening =)
• [ ] _final_output is never used? Should it be initialized to '' so you can start appending to it right away?
• [ ] Probably don't need to filter(None, found) as you already check [item for item in found if item]