LP#1321429: Use server-local time as best-guess

When first calculating the shelf expire time, we assume "now" as
the starting point by calling DateTime->now().  However, that gives
us the time in UTC.  That's not good because closed dates are stored
timezone-aware.  Instead, ask for server-local time.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Ben Shum <bshum@biblio.org>