Fix radosgw actually reloading after rotating logs.

The --signal argument to Debian's start-stop-daemon doesn't
make it send a signal, but defines which signal should be send
when --stop is specified.

Signed-off-by: Jan Harkes <jaharkes@cs.cmu.edu>
(cherry picked from commit 44f1cc5bc42f9bb6d5a386037408d2de17dc5413)