defect/de-26 -- OnDelivery() reprocessing failed comms events files

nparcel/b2cconfig.py
nparcel/conf/nparceld.conf
* replaced "pe_loop" with "on_delivery_loop" as per previous refactor

nparcel/service.py
* new method flag_comms_previous() that checks if the comms file flag
  has already been set

nparcel/ondelivery.py
* updated the process() method to ignore skip execution if comms files
  already processed