rgw: Reduce data sync parallelism in response to RADOS lock latency

rgw: Reduce data sync parallelism in response to RADOS lock latency

Lock latency in RGWContinuousLeaseCR gets high enough under load that
the locks end up timing out, leading to incorrect behavior.

Monitor lock latency and cut concurrent operations in half if it goes
above ten seconds.

Cut currency to one if it goes about twenty seconds.

Signed-off-by: Adam C. Emerson <aemerson@redhat.com>