rgw: raise debug level on redundant data sync error messages

rgw: raise debug level on redundant data sync error messages

each of these errors have already been logged at a lower level with a
more detailed error message. by logging them as ERRORs at level 0 here,
the messages could be easily confused as separate failures

Fixes: http://tracker.ceph.com/issues/36037
See-also: http://tracker.ceph.com/issues/35830

Signed-off-by: Casey Bodley <cbodley@redhat.com>
(cherry picked from commit a6e392f2b8cb885f6fede5dfa9b584659740e161)
Signed-off-by: Matt Benjamin <mbenjamin@redhat.com>