ENYO-2405: fix global-var leak + misc minor edits

- variable _fn_ was leaking  ion global scope.   A possible  cause of
  name  clash when  several packages  were downloaded  simultaneously.
  Also renamed is `fileName` as it is more descriptive.
- replaces (^J^J^J+) by (^J^J) (at most)
- remove outated comment
- use `.bin`  as a  fil extenstion when  unknown from  the associative
  array.
- make a trace more explicit (start streaming...)

Enyo-DCO-1.1-Signed-off-by: Francois-Xavier KOWALSKI <francois-xavier.kowalski@hp.com>