task/ta22-21 -- creation of staging directory

nparcel/conf/nparceld.conf
* set the base directory to /var/ftp/pub/nparcel

nparcel/config.py
* new attribute "staging_base" location to place processed collected
  reports and signature files for further processing
* method parse_conf() update to slurp "staging_base" config item

nparcel/exporter.py
* method get_collected_items() argument update from "business_unit" to
  "business_unit_id"
* report() method is now Business Unit aware via "business_unit"
  argument

nparcel/exporterdaemon.py
* expand exporter object in _start() method to accept "staging_dir"
  argument
* call to report() in _start() method now accepts a "business_unit"