Bug 12063 - Fix QA failures

Bug 12063 - Fix QA failures

  - Remove expiration date calculation in C4::Letter since it's done
    when setting the reserve waiting,
  - remove expiration date calculation in circ/waitingreserves.pl. Use
    the one in DB,
  - add a new atomic update that calculate expiration date for
    waiting reserves,
  - add tests for days_foward function and fix the infinite loop.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>