rgw: RGWPeriodPusher uses zone system key for inter-zonegroup messages

RGWPeriodPusher was using an empty RGWAccessKey for inter-zonegroup
messages, which were rejected as an anonymous user with 403 Forbidden.
this prevented multi-zonegroup configurations from converging on the
same period configuration

Fixes: http://tracker.ceph.com/issues/39287

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit f97be8c)

src/rgw/rgw_period_pusher.cc

@@ -250,7 +250,7 @@ void RGWPeriodPusher::handle_notify(RGWZonesNeedPeriod&& period)
       hint = conns.emplace_hint(
           hint, std::piecewise_construct,
           std::forward_as_tuple(zonegroup.get_id()),
-          std::forward_as_tuple(cct, store->svc.zone, zonegroup.get_id(), zonegroup.endpoints, RGWAccessKey()));
+          std::forward_as_tuple(cct, store->svc.zone, zonegroup.get_id(), zonegroup.endpoints));
     }
   }