rgw: s/idle_timeout/default_idle_timeout/

Signed-off-by: Loic Dachary <loic@dachary.org>
(cherry picked from da00662191e9ec173be50b551253f4460f369f9d)
Merge pull request #92 from ceph/wip-9126-dumpling

rgw: s/idle_timeout/default_idle_timeout/
rgw: fix up default_idle_timeout backport

Two things:
 * argparse was used but not imported
 * idle_timeout was in config but not put in apache conf

Signed-off-by: John Spray <john.spray@redhat.com>