rgw: change default log level

Fixes: #6554
Backport: cuttlefish, dumpling
Default log level was just too high, bring it down a bit.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
Reviewed-by: Sage Weil <sage@inktank.com>
(cherry picked from commit 8d7dbf85472cfca9268d81ecf057ea078cf345b3)